I can't comment on those prices but they do not look out of line from what info I have seen here in the site.
The act of correctly lining up the ring and pinion gears so that they mesh properly (provide the correct contact pattern) is a skill in itself. If you have Service Manual, reading about it might scare you off as much as rear end "how-to's" did me.
This is one of those times where I went straight to an expert.
It is too bad that you do not have the supply of donor vehicles handy so you could just swap out and entire axle. Yes, this is something that you could tackle down the road.
2012 Mustang Boss 302 #1918, Competition Orange. FGF replacement 2006 Mustang V6 Pony, Vista Blue. Factory ordered. 2019 BMW X3 (Titled to the wife, but I'm always driving it for her. So I'm claiming it) Old projects, gone but not forgotten: 1967 FB 400, original CA car. After 22 years of work, trashed by the guy who was supposed to paint it. I had to sell it. 1980 Turbo Trans Am 1970 Mustang fastback, 351C 4Bbl, auto 1988 Mustang GT, 5 speed 1983 F-150 4x4, built 302 1994 Chevy K2500 HD 4x4, 454 TBI
