Taxi is best
I agree with the other guys, it is best not to rent and drive; do take a cab and/or a bus.
As Americans, particularly those from the western states, holding on to and protecting your wheels is like holding on to and protecting your privates. An automobile is not necessarily an extension of one's persona.
Think of it like being in a major city like New York City or San Francisco: it is much easier and far more convenient to take cabs and or public transportation. Quite frankly it is more cost effective (both time and money) to take cabs and public transportation.
Frequently I take the bus and/or taxi cabs and I live here, have a car and know the geography fairly well.
Unless you have an obvious and compelling need to rent a car, DONรขโฌโขT. If you ding the rental car, or even if you didnรขโฌโขt and they say you did, you are on the hook for the repairs. Moreover, it is almost impossible to travel to Jaco or some other destination without getting a ding.
And driving in Costa Rica can be more than a challenge particularly if you do not know where you are going. Costa Rican maps are crude at best. If you are trying to find something you will discover there are few streets, and if there is a street sign it is small and easily missed.
Directions are given by selecting a "landmark" such as the Mercedes Benz building and then explaining that you should go 100 meters north and 200 meters west. But they may or may not tell you that the Mercedes Benz building is really the Scotia Bank building.
Take a cab. It will reduce your grief factor tremendously.