hey man,
im actually doing a 300zx brake upgrade myself… but only the fronts. anyways, just go to car-part.com and get them used, i picked up mine for $110 CDN shipped from some wrecker in the Illinois, and there are a few places where you can get them fully rebuilt, i’ve got quoted $60-$80 for a rebuild (each) or for rebuilt calipers + core… so thats about $230-$250 for fully rebuilt calipers, i dont necessairly know if thats good but its probably about the best you will find. hope that helps!