Used Cars: legal interest rate, kelly blue book, better business bureau

Question
We recently just purchased a 1996 Ford Mustang from a local used car dealership. Originally the salesman told us the car was $6000, which seems about correct being that the Kelly Blue book said about $5100. But after putting down $1500 and signing the papers which they kind of rushed us through because they were closing, we did not get copies of the paperwork a week later when we went to make a payment which we were told would have been $100 a week for 50 something weeks. When we got the papers it now said $100 a week for 150 weeks, and the total price of the car was now $14000. We complained about this and were told that this was the cost with interest. That would be about 150% interest!!!
Is this even legal and how do we get out of it????

Answer
Sorry for the late reply, I have been out of town on business. I thought I had set the vacation dates with the allexperts website, but apparently did something wrong.

You can ask to see that paperwork you signed.. if it says you agreed to the terms which lead to the car costing 14000 in the end (which is ridiculously too much) - and you are certain they told you it would cost something different - You MIGHT have a legal case... since they cant tell you one thing and give you something else.. (although technically it is your responsibility to read anything you sign... car buying is not a simple thing you should ever rush through.. closing or not.. come back the next day...) - Speak with the manager or owner of the dealership... explain the situation.. don't call - go and talk to him/her... if they refuse to help.. call a lawyer... I wouldn't rest until I got it resolved.. sounds like they scammed you if you ask me. If you can't afford a lawyer - call the better business bureau in your area.. they can actually take them to court for you...