There are many good posts about renting a car on Tripadvisor but many are not entirely accurate or simply incomplete. Here is what I could recommend and provide:
1) Renting a car in CR is not like renting a car in N. America or Europe. Keep in mind, you are in a foreign country and we need to respect that.
2) Are you going to drink? RED color taxi could get you around anywhere in SJ for $2-$4. Excursion tours usually provide readonable transportation, so you could have a good time, drunk or not.
3) Taking public transportation such as buses will require you to speak some Spanish and know where you are heading.
4) Most Costa Rican taxi drivers speak English! Don't need to use orange taxis at the airport. They charge more for the same service.
5) Price of rental cars vary hugely at first look. In the end, they are usually about the same. However, most big car rental companies have hidden charges and have histories of playing "bate and switch": they would offer you a size of car but then become not available at checked in unless you ate willing to pay more. You would end up either spending more money or waste a lot of time despite you have a "guarantee" reservation. Worse is when they don't honor the on-line booking price because it's a "computer error". And complains will not get you anywhere with car rental companies.
6) Some car rental companies are worse than others: (noticeable bad reviews from other Tripadvisor members are Payless and U-Save). Be careful with your choice before giving your credit card number out. Cancellation policy may include a small processing fee)
7) Wild-rider and Vamos are excellent as pointed out by many Tripadvisor members. I concur!!
8) Parking is not easy in SJ, most are paid parkings. Good luck to find your car if it's towed.
9) Potholes are everywhere in SJ! Their sewage is over-ground, so there are DEEP trenches on both sides of roads and watch out for turns. Your back wheel may end up in the ditch/trench/sewage drain. Highway roads are good. Mountain roads could be rough for cars.
10) Don't speed, tickets are extremely expensive ($600 for 20km over) and the police are everywhere on the highway. Most area have speed limit between 40-60KM (not Miles).
11) Radar detector is illegal in Costa Rica. Not sure what the penalties are if caught...
12) Mandatory insurance or 3rd party liability or LW insurance is required by Costa Rica law. It's not LDW/CDW (which I will provide more details next). There is NO exception and most car rental companies are not up front with it. For example, Avis, Hertz or Budget don't even have it as an option at their Internet booking. Vamos and Wild-rider include the mandatory insurance in their quote. It's usually $15-$25 a day. Remember, it is different than CDW/LDW! If it's not in your quote, you still need to pay for it before you pick up your vehicle.
13) CDW/LDW is the optional insurance. The renter could use their credit card coverage but MUST bring a proof of coverage from your credit card company. i.e. an agreement from the under-writer or a letter from your credit card company. They won't take your words for it. Some credit companies do not provide coverage outside of North America.
14) If you are using your credit card car insurance coverage, they will put a $1200 to $5000 on hold on your credit card (all car rental companies do that: good or bad). It's their "policy!" Make sure you have a high credit limit to cover this. It's not an extra cost but it's a high limit hold!! Many travelers end up not being able to rent a car because of low credit card limit or under budget. There's no negotiation.
15) If you choose to purchase their CDW/LDW, they will still put a $750 to $1500 on hold on your credit card. The reason? Tire damage and vandalism are not coverages even if you have full CDW/LDW coverage. Again, make sure you have a high credit card limit.
16) There are un-expected speed bumps near houses even in the middle of highways. Watch for signs.
17) Road signs are ok. You will need a navigator to help you, especially at night. It's quite easy to get around Costa Rica.
18) Most bridges are a single lane, watch for signs to indicate "right of way". It's not first come, first go!!
19) Get an updated Costa Rica GPS map or a paper map. You will not be able to punch in exact addresses in Costa Rica most of the time. i.e. a place is across the street from a church and near a gas station. How are you suppose to punch it into the GPS? Instead, use landmarks or simply drive into a town by following direction from your GPS or a paper map. Then, punch in the landmark near your destination. Get an un-locked phone, it will really help with finding directions. Most Costa Ricans speak decent English.
20) Newer highways require tolls and use them!
21) Roads between towns (except for highways) are narrowed and hard to drive. You need be able to stay in your own lane, especially if a huge truck is coming from the opposite direction. There is little shouldering room available (if any).
22) Get a 4x4 if you are planning to go up mountains because a car is simply not good for muddy and/or rocky conditions.
23) Many cars/SUV are manual drives (stick-shift). Confirm your reservation with an automatic if you have never driven a stick-shifted car before or not a good stick-shift driver. There are MANY hills and windy hills. Imagine San Francisco!! I am not exaggerating because I used to live there and drove a stick-shift.
24) Get a car/SUV with adequate horsepower because of the hills or you will have someone on your tails or trying to pass you all the time. Don't cheap out!
25) Remember to bring towels if you plan to visit beaches or play water sports. Otherwise, you will have to deal with wet seats if you don't have changed if clothes!
26) Lock your car and put away your stuffs (such as GPS or cell phone or even their chargers) at all time!!
27) Don't pay for someone to "watch" your car. They don't!!
28) Close your windows even on hot days because of thieving issues and animals will go in your car if they see food! Seriously.
In my opinion, it's a lot of fun to drive around Costa Rica and it makes sense most of the time. Public transportation is good within San Jose. But if you really want to "explorer" Costa Rica in "your own pace", renting a car is a GREAT option.