Seriously.. in general. Motels are as cheap as you need them to be. A one bed motel room off the highway can cost you anywhere from $35 a night to $110 a night.
I say just drive and wing it. When you start to know you are going to get tired. Look for places along the route. Not the best way to plan a trip, but it adds to the excitement.
And you could come home with some cool stories about finding a place (As we did when we drove to Missouri. when I was younger - oh the places we found.
)
Also, a great place to find deals is the local rest areas. They have a book up in this area called
TRAVELER Discount Guide Hotel Coupons. It's available nationwide and you can use the webpage link to find a distributor of the guides. But I have found them at all major rest stops (ie: not picnic areas)
Good luck in your planning (or lack thereof).
edit: We're not going to FL. Not for a mini-comp anyways. Sorry.