Honestly, I know it sucks but there's not much you can do. If you get it, it'l be the first thing they take away if they get pissed at you. The only thing I can recommend is to do odd jobs or chores and earn your own cash, and spend that as you like. It totally sucks being a kid, I understand, but circumventing your parents never turns out well.
Study hard, do well in school, behave, and set yourself up for a good future. If you do that then when you're an adult you'll have all the opportunity and means you can handle to get yourself nice stuff then.
I'd stick with cheaper DIY builds for now, then you can "sell" the idea to your parents that you're learning hands on electronics and manufacturing.