Sibyl you can tell your parents and ask them not to tell anyone else. I told my mom and she didn't tell anyone until I was much older, and they've never brought it up to me.
Scemoboy, as mentioned, it doesn't need to be that expensive. I started out at 15, I had an old blank notebook and a copy of Wicca for Life. The candles I either borrowed or bought at the dollar store, my athame I bought at a farmers market for 5$ and slowly I built my collection of tools. I think books are what most of my money went to. My altar has never been a fancy one [dark stained wood is my dream altar] I have used filing cabinets, coffee tables, large stones, and currently a plastic box. If the area is concecrated that's all that matters. My first circle had candles and incense, my BoS, cake and juice, and me. It wasn't special, but I still remember the feeling of that first circle. It's your intent, not the 100$ athame or gold edged Book of Shadows that makes the circle.
Regarding your parents, just talk to them. Be calm, ask them to listen to everything and think about it. Present them with facts and reference information. Be prepared you might have to compromise.