First, I'd respect the wishes of your parents. No one knows the financial situation of your family like they do. Trust their judgement. At the end of the day, they're the ones you can truly count on to ALWAYS be there and steer you in the right direction despite what others may tell you.
Second, if this is really important to you, perhaps you could speak with them about the possibility of getting some after school work or maybe do some things around the house for some hobby money? The key is to be upfront and straight with them from the get go. If you're honest, respectful and sincere in the approach, I doubt your folks would say no. It certainly would be a sign of maturity which I think they'd respect.
Finally, even when you get off on your own, one very important lesson will be self restraint. Spur of the moment purchases and quick, ill thought out financial decisions can really get you into trouble. Best advice I got from my pops is forget the credit cards except for emergencies. Pay as you go. If you ain't got the $$ on you, you don't need to make that purchase. Good advice especially for young buyers like yourself.
Good luck and remember...your folks are on your side and only want what's best for you. Trust them. You may not like it or understand now, but it's the best thing to do.