figure out a way to make money and earn it for yourself. if you cant even afford to buy a car who is going to pay to insure it? Put gas in it? Register it? Having a car is a privledge-not something parents are obligated to provide for you.
Get a job or do work of some sort & offer to go half on the cost. Cars & the expenses that go with them are very expensive. Esp. insurance. Expecting your parents to continue paying the full bill for everything you want is a little silly, esp now that you are old enough & responsible enough to drive.