I booked my car with Charlies car rental. It was about $25 a day + insurance. It ended up being like $40 a day... still thought it was a good rate.

Check hotwire.com specials.Also check if your car insurance will cover while in PR and bring a copy of the insurance policy. That will slice off some $ of the car rental cost (insurance). Also check in any of your credit cards, covers car rental insurance while traveling when the cost of the lease is paid with them - such as with American Express.

The hotel charges $15 per day for parking, unlimited in/out, but still you'll be saving a lot, in tours, food, if you can do that without using the hotel's restaurants 7 pre-planned tours,which each will cost you more than a day's car rental per person, and as a bonus, you'll be able to move around freely, at your own pace.