I watch 3 mustang/ford forums that seem to have a little more "sane" pricing on the stuff. You have to be careful because there are a lot of shade tree mechanics on these forums who's idea of "good shape" is a far cry from mine. They also have no clue about what the term blue printing is either and if it says it is for a SBF they slap it together and hope. So if you get heads or anything that needs a flat, non-warped surface, I would highly recommend taking them to a reputable machine shop and have them given the once over and assume nothing.
The forums I watch are:
StangNet NMRA Classifieds Corral.Net Classifieds
Lynn