Is there any MTB out there that rides like an old school BMX bike? Like a racing BMX not a trick bike.

I've gotten so used to my road bike that it's become boring. I want to be able to go for a ride and jump some curbs and knock over some cans with a kick out now and then. I can't do that with my current GT idrive that weighs about 400 lbs. (or at least if feels like it does) Plus I have to hand crank the spring about a thousand times to stiffen up the suspension so I can ride up a hill without to much powerloss.

So I guess the question is whether there are any super light and fun to ride MTB for under ....12-1400 bucks???

p.s. Why are MTB bike wheels so tall? And why are BMX wheels so small?

p.s.s. I don't ride trails so I'm talking about city riding, like through parks, on grass, curbs, lawns >__< etc...