Race bikes can be reasonably specific, if you go for an aluminium or carbon monocoque type thing, but they'll stil hold up to smooth trail/jumping use. Probably better to go for a cromoly race frame, as although it may be a little bit heavier, it should hold up better if you're a bit heavy handed.
Top tube length is pretty crucial, as something too short feels awful. I'm 5'10ish and run a pro xl length frame with a 21.3ish top tube.
Prices? whatever you want really. My Brew frame was £300+ so total build around twice that i guess, Dialleds frames are nice if you want to keep with a 'familiar' stw friendly brand. Second hand or complete builds are where the value are, and now may be a good time, as new models are out and people are swapping bikes.
If you're a bit too tall, or 20" is a bit too much of a shock you could get a 24" cruiser. And unless you're really smooth/skilled, keep the clip pedals on the mountain bike!
