Ah shit, man. That sucks.
Not sure if you plan to do the work yourself or take it somewhere, but Baertrax in Dallas regeared my '89 Jimmy a couple years back, and they seem to do solid work. I did the break in, changed the diff fluid, then immediately drove to Silverton, CO, did the Alpine Loop, then drove right back. No troubles with the new rear end at all.
Rear differential regeared to 4.10 (with two new axle shafts and all new bearings/seals) ran approx $1600 OTD if I remember correctly. However, I did buy and provide my own ring and pinion gear set, so you'll have to add that to the $1600. You might save about $500 if you don't need new axle shafts.
Did they give you vaseline before they bent you over!!