I say 30-45k for a good one but depends on the engine mods. (single or twin plugged, what kind of elec. ignition, pistons, cylinders rocker arms etc..) and body (steel, FG or CF.) also to consider brake upgrade and suspension.
So each car has very particular price. Cris h used to have good cars for around 40k
http://forums.pelicanparts.com/showthread.php?threadid=154473 but I remember the race group sold one for 80k so it's very dificult to answer your question.