One great advantage of renting a car is that you can visit many of the secluded beaches and mountain areas. And with the power of the Internet, you can now rent just about any vehicle online and have it waiting for you when you arrive.
For 350-700 USD a week you can rent a econocar/mid size 4WD. Insurance is the majority of this cost and it is not optional. Four-wheel-drive is good for extensive traveling outside the Central Valley, especially in the wet season. In the dry season going from La Fortuna to Monteverde via a direct route was over a boulder strewn 15-30 MPH road. Four-wheel-drive was also useful on the Nicoya coast.(above based on 2001 roads). It's often possible to rent a car with a local driver from the various tour companies, if driving yourself seems a bit daunting.
Due to the condition of most roads outside San Jose, car insurance, even with a zero-deductible option, generally does not cover tires and rims. Car rental companies require a guaranty deposit from 750 USD during the rental period and a credit card is necessary for this process. Using an insurance program provided by some types of gold or platinum credit cards is a good advantage, since these credit cards would cover small scratches, small dents as well as the entire rented vehicle in case of collision or theft.
