I paid $194 for my 31 spline trac lok new. rebuild kit cost $50 the diff is going to cost you something so you just have to decide if it is worth loking around for it.
the new 3 pinion tru trac is supposed to be stong too but it is $435 and there will be some extra noise at it is gear driven LS.
to me the four viable options are
trac loc ~200
carbon fiber clutch trac lok (cheaper than eaton) ~300
tru trac (3pinion) ~$435
torsen (very expensive) ~$550
used 31 spline and rebuild kit ~100?
auburns are not rebuildable. the eatons are nice but are breakable and expensive. better off just buying carbon fiber trac lok
Find somebody who bought one, but doesn't have a use for it after all and they're selling it for less than they paid for it just to get it off their hands