I used to do this a good bit maybe 10 or so years ago. Have been watching the deals in years since and they've been slipping quite a bit vs. before. Used to be you could get around $8/day with minimal taxes and up to 2 weeks keeping the car (and no drop charge, of course). Nowadays you're likely to get a higher rate, many more taxes, and much tighter maximum lengths.

With gas prices what they are, you'd also figure on 10-11 cents gas cost per mile (much worse if you took an SUV or other gas guzzler). A one-way to the Northeast could easily run $80-100 in gas, which is quite beatable by air if it's a Florida route with a lot of LCC competition.

I think you'd need a solid plan (i.e. more than 1 person & wanting to hit a specific intermediate spot) to make it work. Even then, they might try to box you in with maximum lengths.