Parents won't let me get more into mountainbiking

So for the past few years I've been really into mountainbiking, it's a great sport and I spend a lot of time outdoors doing it. Recently I've noticed that my bike has been just holding me back from progressing further and I was stuck with my skill level for a pretty long time. My parents never really liked me doing that sport so getting a new bike was always a challenge. I've seen a few nice bikes on sales in pretty affordable prices, I want to ask my parents if I can get one but I'm scared that they'll end up yelling at me. Any help?