Are you looking for teh cheapest option?
Your best bet is to find out what the ratio is, and assuming it's a factory one (4.10, 4.30, 4.56, 4.88) look up the part on car-part.com and just order one from a junkyard.
Don't be afraid to do a whole regional or even national search, there are yards that sell them for$200 and ship to you for another $30 or so.
The lin kabove shows how to get the 3rd off the truck, pretty easy. Biggest pain is (a) disconnecting teh brake lines and (b) breaking the seal between the case and axle housing so it'll come off.

With 200+ Billion electrical parts, the world most complicated machine is inside your own skull.

Question Reality.
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'89 Rnr DLX "SR4.5", 32s w/ 5.29 locked f/r blah blah