The dealer can charge whatever he wants for the cars he is selling. His job is to make as much money as possible on the sale of a car. Everyone who buys a used car knows this. Next time you go to a used car lot you should bring a copy of the Kelly Blue Book so that you know what the approximate value is of the car you're thinking of buying. If you didn't do that, and they managed to get 2x the Blue Book value out of you, one can only say "my condolences" and "caveat emptor" (let the buyer beware).
I am not licensed to practice law in Michigan so the foregoing should not be taken as legal advice, but simply as information based on general principles of law which is intended to educate. If you need legal advice, please consult a lawyer who holds Michigan licensure.