And that's exactly why a 14 year old shouldn't be making decisions like buying a car- I'm confused as to why all your posts say "WE" when your mom is the adult - it's her say. If she isn't capable of making decisions like that - then you need an intervention more than just with your pets. Which brings up a burning question that I know bunches of us have wondered but I'm not going there.
Good Luck - I really do hope you find a car - altho it might not be the car YOU want.