When you fly into Costa Rica you are actually arriving into Alajuela, which is a small town outside of the capital (about 20 minutes).
Rental cars
There are a lot of options, I have used Avis, Hertz, Budget, Thrifty, Payless, and Europecar. My favorite is Thrifty, followed by Payless, Avis, Hertz, and Europecar. Europecar was fine... just too far from airport for my liking, and Hertz is usually prohibitively expensive.. I am using payless on this trip. I do not recommend eoncomy car or Budget rent-a-car, Economy rent-a-car did not honor my reservation at Christmas, they promised something everyday for almost my whole trip and never came through... I was 30 minutes late picking up my car. I booked a make-up reservation with Budget, which came through and I had a confirmation number. They would not even open up the gate, unless I had a pre-paid reservation.
The main thing to be aware of is that you cannot avoid insurance, which can run $15 to $30 a day, I was almost robbed last year while in my car and at the time paid for full coverage, which I have done each subsequent time as well, but costs $25 - $30 a day. the rental is usually around $15-25 a day, so it adds up.
If your credit card provides CDW for international rentals (check, because not all do), then you can save about $ 5- 10 on the insurance... but you are still required to get insurance.
You DO NOT need 4-wheel drive, unless you plan on going way south or way north (i.e. more 4 hours in either direction). Almost all of the car companies offer an "Economy" car that is too small to be practical, you will most likely want to go with a "Compact" (Toyota Yaris) size. or larger.
One thing I recently figured out is that when you reserve your car in the US online, you are quoted a price in dollar. When you are quoted a price for insurance you are quoted the price in dollars. The taxes are quoted in dollars, but when you return your car and check out, the price is converted to costa rica currency (colones) at a ridiculous rate. I rented a car for 2.5 weeks from Economy rent a car this summer and the difference between what I was quoted and what ultimately hit my credit card was $92. I looked back at my old records and Thrifty charged me in dollars, which is what my reservation was quoted in, no difference.... so you need to factor in about a 15-20% overcharge with Payless... because, you pay more with Payless.
Driving in Costa Rica
I have never had an international driver license and it has not been a problem. I have been pulled over a couple of times, I was not given a ticket either time (just lucky I guess), I did not offer any bribe either, which they say is not advisable.
Driving in Costa Rica is not bad in general, follows most of the same convetions as United States. Driving in San Jose can be intense, but in general, it is fine. On long trips to the coast or elsewhere, you need to be very alert to people passing you or others in oncoming traffic on blind hills and blind corners. I have had buses pass me on blind hills driving from Puntarenas.
Also, when leaving the rental car company be very alert. A popular scam there is for someone to punture your tires at a traffic light soon after leaving the rental car agency, then follow you until you realize your tire is flat. When you pull over, they offer to help and then rob you. Happened to me in summer of 2009, fortunately, I stopped at a fruit stand to buy fruit quickly after it happend and before my tire was even flat; someone else stopped to tell me they had seen the people in another car puncture my tire. I was very close to rental car agency, so I went to service station, refilled tire and then switched out car at rental office. I had heard about this scam, but this was the first time that anything close to this has happened to me in the 12 years I have been going to Costa Rica.
Also. Do not drink and drive. They are all over it, especially for tourists.
cheers.
Places to go:
Start in San Jose Area - 1 night in hotel (there is a Hampton Inn about 1/2 mile from airport and shares parking lot with rental car companies). If you arrive in the evening (after 5:30 pm), I would not recommend renting a car until the next morning. Roads are not welll marked and you might have trouble finding your hotel at night. Get a taxi to your hotel and pick up your car in the morning. Ideally, arrange with your hotel to pick you up at the airport. There are official red taxis you can get at the airport. I have never used one as my family always picks me up, but they have meters, If they don't or don't want to use them, or claim they do not work, then make sure you agree on price up front, however, be prepared when you pay for them to ask for a couple of dollars more when you pay (drives me crazy, I don't know why they do that). Currently $20 dollar is about 10,000 colones. You out to be able to get to any hotel in Alajuela or San Jose or even Heredia for 20,000. Hampton Inn might be 5000.
By the way, there is an ATM in the luggage claim area of the airport. This is a great time to get some local currency. Very safe, and you generally get good exchange rates via your bank.
Day 2 - San Jose central market, Jade museum, Gold museum, shopping (treat San Jose as you would any major city - don't be flashy or foolish, stick to tourist areas - think New York City in late 90's, don't wear much if any jewelry). I really like the San Joe central market area and the plazas, but I haven't spent a lot of time there. I have been to Gold museum, but not Jade museum.
Day 3 - Drive though downtown Alajuela and up into the Poas Volcano area - first go to the Poas Volcano - about 2 hours from downtown San Jose - Look for places along the road to have Breakfast once you are heading up the mountain. There are some good places after Savanilla and before Poasito. Have lunch at the La Paz Waterfall gardens, do the tour. If you have time, swing back to Savanilla for a real coffee tour at La Doka Estate. Buy a good supply of their coffee - it is the best. Have dinner at Colbert's (French/Costa Rican cuisine - it is outstanding. Stay the night in the Siempre Verde Bed & Breakfast (http://www.siempreverdebandb.com, (I have not stayed there, but it is reasonably priced compared to some other options and looks beautiful - this is about 40 minutes from airport, so it is also an option in lieu of Hampton Inn. It is also in the middle of a massive coffee plantation. Another option is at the la paz waterfall gardens http://www.waterfallgardens.com/ (have not stayed here either, but the place is beautiful, we have visited many times - it is ridiculously expensive for Costa Rica). There are a lot of road side cabinas in this area, I have used them, but they look cute. There is one very close to Colbert's Restaurant (feels kind of like the North Carolina Blue Ridge Mountains in this area - very nice. Be sure to check out the fruit stands.
Day 4-5 - drive to Volcano Arenal - about 3 - 4 hours from Poas. Take a tour of the lake, check out the Tabecon hot springs and spa. Find someone to take you on a hiking tour around base of volcano. The Tabecon hot springs also has a hotel. Someone from my office stayed there and really loved it. I have been a few times. Once we stayed in a resort about 45 minutes from the the Volcano in a resort called El Tucano http://es.occidentalhotels.com/hotels/ElTucano.asp . The other times we stayed in very small hotels that we passed on our way into the town of La Fortuna, which is at the base of the volcano. The town was renamed to The Fortunate, after the volcano blew out on the side opposite of the town and wiped out another community many years ago.
It is often cloudy here and you have to be lucky to see the volcano... it pours lava out of the top and blows rocks out as well, the most I have seen is a red glow at night. But there are natural hot springs all around and there is a large lake which offers boat tours.
Day 6 Drive to the Monteverde Cloud forest - get a reservation for a hotel there and fill up on gas before going up the mountain - never know about the gas supplies there. I have been once... it was neat, kind of a hippie artist refuge. Originally founded by quakers from the US in the 1950's. Has a nature refuge and a lot of interesting art shoppes and gallaries.
Day 7 Pass the day checking out the National Park in Monteverde and enjoying the artist village atmosphere.
Day 8-10 Drive to Manuel Antonio National Park - Be sure to check out the Bar made out of a B-52 bomber perched at the top of the hill coming into Manuel Antonio (you will need reservations here - very popular place. Spend a day checking out the sites in Manuel Antonio outside the park and in the surrounding town. This is my favorite beach in Costa Rica. This place looks like the perfect white sandy beach with palm trees and blue water that people think of when they think of paradise. The town is very cool as well. There are a number of resorts and hotels in the area. On your way into the town of Manuel Antonio, you pass through the town of Quepos. There is a Best Western hotel http://www.kamuk.co.cr/looks very nice, it has always been sold out, and we ended up staying at a hotel around the corner called Hotel Melissa or the one next to it, Hotel Malinche, both were cheaper, clean, and safe, but definitely no frills. There is also a pretty good restaurant around the corner from Hotel Malinche that is facing the beach (http://www.elgranescape.net/restaurant.html). With both Melissa and Malinche, the reservations were made in Costa Rica on the phone the day we were leaving for our trips by Costa Ricans.There are a lot of hotels to choose from, these are just the ones I am familiar with.
Spend at least a day in the National Park - get there early and avoid the lines - they limit the number of vistors in the park at anyone time. I have not been for a couple of years. The last time I went we had to wait in line to get into the park. I heard about someone else who went at Christmas and never made it into the park because of the limit on the number of vistors in the park. So it definitely pays to get there early.
Day 10-12 drive to Jaco beach (North back the way you went) pay for surf lessons from one of the hotels there. I have never stayed a single night at Jaco Beach but I have gone there for the day and surfed there. Not exactly in Jaco Beach, but in the area. A quick search of google and you can find a lot of options for Jaco. there is also a Best Western in Jaco that I have heard is nice.
Day 13 - Drive back to San Jose - about 3 hours. Pass the day in San Jose - if you missed central market - this would be a good time to go and pick up souvineers.
Day 14 - Fly home.
An another option if you just want to go to a resort or to the beach is to go to a resort. I have stayed in three in the area, Hilton Double Tree in Puntareanas (Formerly La Fiesta). I was there last, it is my current favorite, it is also all inclusive. The beach itself sucks, but the resort is great, food is good lots of activities, a little casino, a night club. The pools were amazing. Another option is the Marriott Los Suenos resort. I have been once about three years ago. It was not all inclusive, but it was beautiful. It was very new at the time and has a golf course. However, at least when I was there, there was abosolutely zero to do except for lay by the pool, work out in the gym, or play golf. So in the evening there was nothing to do, they did not even have nusic in the bar. We were very bored there. The third resort is Tambor, which is you can only reach by taking the ferry from Puntarenas to Paquera and then driving about 20 minutes down the coast. I have stayed there few times. It is nice, but getting a little dated, also all inclusive. Food is ok, facilities are nice, pool is nice. Beach is pretty good. Some activies onsite. There is a nearby golf course. There are several resorts in Guanacaste (about 4-5 hour drive northwest of San Jose, I have not stayed in any I am crazy about, but I have also not stayed in any expensive ones. There is a resort called La Conchal, which is beautiful, but alos very huge, I have been to the beach which is made up of tiny white sea shells, almost no sand (beaches are open to public in Costa Rica). There is also a Four Seasons Resort in the Papagayo area, have not been, but passed by it in a boat, looks incredible.
This is just a part of the central valley and pacific coast. I am less familiar with the atlantic coast, but you could make a good 6 day trip out of Limon, Cauhita and Puerto Viejo. Also, you could skip the vocanoes and add more beach time on the Pacific coast by taking the ferry from Puntarenas to Paquera and driving along the coast to Montezuma-spend a couple of days there and a night or two in the area around Tambor. Costa Rica is pretty safe, especially compared to the rest of central and south america., but be aware of your surroundings and your belongings. Don't leave luggage where it is visable through the windows in your car, make sure you always lock your car and park it a regular well lit parking area. I would recommend getting the full insurance on the car rental (you have to pay almost 65% of the full rate anyway by law, so you might as well be fully covered.