Autotrader is a very good option, Have you considered taking it over to CarMax? They usually are willing to give a little more than most used car resellers especially if you return it to stock and the milage is low.

Get something slower and safer. Your still to young for that car. Trust me, whan I was 16, I would have been in the same situation, and I had access to some wicked twisty roads, so I'm sure that I'd have parked it into a tree.