Drive Out from participating airport and neighborhood locations in Florida.Basically, the deal is that as long as you pick up the car from some location in Florida they need to move cars out of, you can rent it for $9.95 a day and drop it off without paying any drop-off fees. I checked some locations and couldn't find any that weren't airports, but all the major airports I checked (Tampa, Orlando, Miami, Fort Lauderdale, Palm Beach, Fort Meyers) had cars that were eligible for the promotion. Some more research revealed that the maximum rental period was two weeks; if I tried to reserve a car for longer than that the rate went to the normal rather high rate.
Drive In to participating locations in Louisiana, Mississippi, Alabama, Georgia, Tennessee, South Carolina, North Carolina, Virginia, West Virginia, Delaware, Maryland, Pennsylvania, New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont, New Hampshire, and Maine.
I thought about flying into Key West and driving back up north. Key West is as far as you can go in Florida, so that's why I decided that would be a good place to start. This far out, tickets to Key West aren't bad: $185 one-way on US Airways was as cheap as I could find, with more sane routings for around $219 on American. Add that to the $202.08 the rental will cost (after all the fees and taxes, you're actually paying just under $14.50 a day), and 50 or so gallons of gas, and you're looking at about $525 to $550 to fly down and drive back. If you have a AAA card Hertz knocks another $15 off the two week rental, so if you have that you can do this for just over $500.
Obviously you have to eat and stay somewhere. Key West in particular has some pretty outrageously high room rates. It's also cheaper to fly to one of the larger Florida airports, so if you didn't care about the Florida Keys you could pick up a car farther north, which would also reduce your fuel cost. If all you wanted to do was to Cannonball Run your way up, you could certainly do it in two days.
Alamo is running a similar offer, at similar rates, but their maximum rental period is three weeks. However, you can't combine their deal with any other discounts the way you can with Hertz's AAA member discount.
All in all this could be a neat little two week road trip up the East Coast, particularly if you have friends to share driving.