I used Costco, we rented a Chevy Impala for 9 days for $203 during spring break from Enterprise, Costco offers all the major rental company's.
One word of warning, Florida has a lot of toll roads, and if you use the sun pass option make sure you read the small print in the rental agreement some car rental company's charge a fee + toll every time you use it, some will charge a fee for every day you have the car even if you are not going through a toll, and others like Enterprise only charge the extra fee the days you use the sun pass (I think $3.95 per day + the toll and a max of $20.00 + the tolls for your rental term)