Yes do a conpression test....after a fresh rebuild (depending on elevation) you should be kicking around 120ish psi. Look for things like chain whack, bent sub frames, and the usual wear and tear. Try and get as much info as you can on the bike.....and it WILL be cheaper to go ahead and find a banshee that has pipes and a few mods already. No sense in spending 3x extra buying all the parts new. Also you want to make sure the guy has a title.
Put up a few ads that you find online and we can take a look at them