ABS Hydraulic Unit tips for rebuilding

I have an 89 Chrysler New Yorker. It has an ABS Hydraulic unit which is rare, and it is not working. The part for a rebuilt one is over $500. The car is hardly worth that. I have had no luck finding one in a junk yard. Wondering if anyone has any tips or instructions for rebuilding? Or perhaps a way to get rid of it and go to a normal vacuum boost, or Hydraulic boost unit? Anyone??