Just do it. If they say "no" just save up some money and buy it yourself. I used to collect dolls and just bought them without caring what my parents thought. Made me happy. That's all that counts.)
You're welcome, Sugarcube. I get it. I'm 22 and my parents give me a hard time about my ponies and dolls, but I just tell them it's my money, I can spend it how I please. It DID take me awhile to get there though. Trust me. XD