I got a steal on mine for $500, hub to hub, including good brakes and shocks. I offered to sell it to another member here (no, it is not for sale, so dont even ask) for $750, and if it'd had a limited slip, he'd have taken it.
the D70s are known for throwing shims, as well as loosening of the spider gears. My 80 has some slack in the spiders as well.
Expect to pay $800-1200 for a good one with decent miles, though some are better at 300k than others at half that. One must keep in mind the calipers on the disc units have a much larger fluid capacity than the wheel cylinders, so a proprotioning valve or master cylinder swap may be in order. Something to keep in mind. For me, the 13x3. 5 shoes stop plenty well.
Daniel