If you have a good underdash unit, and want everything else new, call one of the hot rod A/C shops. Every hot/street rod magazine has dozens of ads for the top companies. They are usually very reasonably priced and know how to modify old systems to work well.
When I upgraded everything on the Squire, it was about 600 bucks. New superflow condenser, sanden compressor, 134 hose kit, drier, triple safety switch, and a 134 compatible expansion valve. I did have to buy a few adapter fitting to hook up to the underdash unit. I made a sanden compressor to york mount adapter plate myself, but they are available as well.
A new sanden unit by itself runs around 200 US dollars.
Rick(wrench)