Another fellow mountain biker here... I definitely spend more time and money on my bikes than with rc's, but I race, so practice comes in handy.
Currently ride a Ironhorse 7point for my race bike... already spent about 6K on it. Next season, I'll be moving up to the Semi-Pro/expert class, so I'm pretty stoked about that. My other bike is a commuter/cross country bike.
BP - If you get really into mountain biking, you should go to some of the local races. Many of them are in Fontana and they have 4-cross, downhill, super-d, and cross country events. Something to consider... or maybe just go to take a look and watch just to see what its like at the races.