Jockey, the good news is that Florida has so much tourism that automobiles are cheap to rent. Food prices are low simply because it's a state having lower cost of living. Petrol is lower, too, for the same reason.
Use this page to check a bunch of cheap rentals at one time:
www.sidestep.com/h/landing?w=rent+a+wre ... oduct=cars
Here are two of the cheaper car rental companies in the US:
www.dollar.com
www.Enterprise.com
Sometimes you can find a deal at:
www.Hotwire.com
You might also search for Rent A Wreck and Ugly Duckling. They rent used cars, once were widespread, but have experienced business contraction during the past 5 years. If they exist, they will be cheap, but not necessarily conveniently located.