Prolijo...I was waiting for you to jump in here
I concur with everything Prolijo has stated with the exception of the cost of a 4runner. A 4-cylinder vehicle with insurance will indeed cost you about $50 per day, but a larger size 4-wheel drive/SUV type vehicle would indeed cost in the $130 range as Hal01 stated.
I've always enjoyed having a rental car there, and never had a problem. I've rented one on perhaps 12 or 13 trips. I've always rented with Alamo, with the exception of Hertz on two occasions. I would recommend Alamo. The only problems I had was when I stayed at the Morazan, which doesn't have a parking lot. The first time driving in CR I was somewhat intimidated, but since then, I've actually enjoyed driving there. Then again, I lived in and drove around Boston for 10 years, so I was
somewhat accustomed to 'wild and crazy' drivers, the circles, etc.
I've also used the Gray Line van/bus service on five or six occasions, and flown to Quepos quite a few times. If I were staying only in San Jose, then I definitely would not have a rental car, but if you plan on venturing outside the city, I would recommend a rental car.