I pieced mine together whenever I found good deals, and was able to build a pretty nice differential.

180$ for the housing (housing,ship,blast&paint,studs)
330$ for the center (3.25 tracloc 31spline 4pin) a steal, and his wife practically delivered it to me
450$ for axles (new 31spline, plus all the stuff like bearings, axle retainers, seals, labor, lugs)
400$ for brakes (MarkVII disc)

1360$ should have been my total, but im probably closer in the 1500$ range becuase of tools and a caliper mishap...

Still alot cheaper than anything else