Marc, based upon him requiring you to pay at the end of each week as he progressed and no contract I'm assuming this isn't a large scale licensed body shop. If it is a licensed body shop you have much more recourse to see if you can get some of your money back. Here's what I would do:
(Disclaimer- this is not legal advise, it's just what I would do)
-Have the shop that's currently doing the work give you something in writing what it's costing you (what ever the amount) to undo the work the other guy did, you want them to explain why they needed to redo it.
-Go to that person (shop?) with that information and request your money back. This is always the first step in any grievance process, you first have to explain your reasoning to the person you feels owe you and give them a chance to resolve the matter before going further.
- If the person (shop) tells you to take a flying leap, you need to consider your next action. If it's a licensed shop I would start there, complain to the BBB (assuming he's a member), the agency that issued the shop's license, and any other consumer advocacy agency in your area. Their contact with him may resolve the issue, if not, at least he now has a record of unresolved complaints and you consider the next step...small claims court. I checked in Florida it's a very simple process, here's the link to get you started:
http://www.flcourts.org/gen_public/family/self_help/smallclaims.shtml
The burden is going to be "on you" so there can be pitfalls in taking someone to small claims court. The court is going to want to know what actions you've taken to try and resolve it before bringing it to the court. The more actions you've take to try and resolve it prior to bringing it to the court, the more "receptive" the court will be to your complaints. You have to consider, he may come back and say that you had him take the "short cuts" in quality because you were short of funds and that you pulled the car out of his ship prior to him finishing it, he may even claim you still owe him money. If he sounds more convincing than you, you lose. Since you don't have a written contract of any kind, you have a steep hill to climb, so have your ducks in a row if you chose to go the small claims court route. Depending how it goes the court may make you pay him money.
Jim