We've rented small 4 X 4s in SJO (Europcar; they brought the car to the hotel (Orchideas) for us early in the a.m., no charge) and in Liberia (Solid). No problems whatsoever. With any rental company, get (then print out) your written estimates (& contract if possible, sent via e-mail (make sure your quotes include ONLY the one insurance coverage if your credit card coverage is standard, and covers CLC; a letter from your cc company that you can print stating that you are covered is a good idea). Also confirm once before you get there. Check your car carefully when you pick it up (take pics of any scratches, dings, etc., inside and out). Of course, always make sure you have a spare and a jack.
We paid ~20/day for a Suzuki Jimny at Solid (LIR): our cc covered CLC, not the CR mandatory liability (that added about $8/day, I believe). Thought it was a very good price, and Solid was very good to work with.

Car rental car be a thorny issue. You should check and double check whether obligatory insurance is included in your quotation. This is $10-$15 daily approximately, depending on the vehicle model. Companies that get good reviews are: Adobe, Alamo, National, Service and Vamos. Economy and Europcar get very frequent poor reviews. There are other companies and often international names which provide rental, but they are not always directly part of the company, instead are run as a franchise and so the service you may have received in one country isn't always reflected. These companies tend to be more pricey too.

I believe I stated all that in my post, without bashing any particular companies. A competent consumer will do a minimal amount of research to judge whether an agency has a deserved bad reputation.

Always I rent my cars with Costa Rica Special Deals. Really good prices and good terms and conditions, Never have any problem with them. Here is the info : http://costaricaspecialdeals.com/car-rental.html