On the lowned probably $450+ for the posi, $250+ for labor, $30+ for bearings a lot more if you do them all, and really it would be a good time to do gears $150-250 for them, $20-100 for the ABS relector to match.
Chance of finding grooved axle shafts which would add maybe another $200+ to the cost of the job, no need to replace them if they are in good shape though, they are plenty strong.