Yes, they can be rebuilt.
A rebuilt unit should cost somewhere in the $800 to $1000 depending upon the unit. The alternative is to call the junk yards for a used unit. I have found that the junk yards tend too get (ask) too much.
The transfer case is relativly simple. If you are mechanically inclined you can do it yourself. I rebuilt mine last year ( cracked rear bearing mount, some misc.parts, and a good cleaning - especially the T/C oil pump) for under $100.