Car Rental: There are many rental companies in Costa Rica; some of them have great rates for the rental. Usually the rental includes the mandatory basic insurance that will cover CDW. You can also include a full insurance if you want.
New Car: Most of the cars for sale in Costa Rica are from Japan and Korea. You may be able to find some American and Chinese.
Used Cars: There is an extended market for used cars in Costa Rica, any how before you purchase a use car be sure to bring a mechanic to prove the condition of the car and guarantee that you are getting a good deal.