I've raced Quarter Midgets, 3 different classes of Stock Cars (will be class #4 next year), and of course r/c cars. I'll be honest, I really don't pay for my stock car racing, I bring in as much money in sponsorships as possible, and my dad covers the rest. BUT, I am very very aware of how much more expensive full size racing is than r/c racing. Like someone said, 1/10 racing costs about 1/10 as much, it's still not CHEAP though. Does r/c have to cost you alot of money??? Hell no! But if you're like most of us, and demand perfection from your equipment, it's not going to be a cheap hobby by any means. It's definately cheaper than most hobbies though, and I think alot more fun! So really, who cares what it costs? As long as you're having fun, you keep spending, I keep spending, Trinity keeps getting richer, etc, etc, etc....
Personally, I don't know what I've spent on this hobby, and I really don't care. When I figure that out, it'll be because I'm figuring out prices to sell everything for and get out of this hobby!