Custom... Well, done right is over a grand for bmx. But, you can be really nice for under 1000 bucks. About 700-900 really. 800? It depends on how far you want to go with things. But, you can avoid some of the things that freestyle riders really look for in a bike, and most frames cost a little less than freestyle. Not all of them though... some cost as much or more.
Just depends on the components and they can push it over 2 grand if you go crazy.
Which, is crazy I think.