For $500 it's gonna be tough to find anything with an outboard that runs. You can find a small boat and trailer leaning behind someone's shed or garage that you may be able to pick up for little to no money. If you're not the shy type, knocking on the door of someone that obviously isn't getting much use out of their rig might serve you well. There are 2 boats in my neighborhood that haven't moved in the 12 years I've been there....those are the types I'm talking about. Craigslist is still a great place for local boats, but you've gotta search often and be ready to jump quick.