I would think if you shop hard, and use the original inside cabin equipment and replace the parts forward of the fireall you could get out for around $600 or maybe even less.

I got my polished Sanden on Ebay for $150, the VintageAire universal line kit with all hose nd connections and dryer for $100, a new 26" tru-flow condensor for $60, maybe $50-$60 or so for some ready-to-bend aluminum lines, $30 expansion valve, a NOS AC selector/controller for $40 and I cant remember what I paid for the clutch switch (<$100). I did spend quite a few hours making up the compressor brackets.