How much does it cost to change the oil seal on the rear end.

If you mean the pinion seal on the rear differential where the drive shaft connects to it, then, that takes about 1.25 hours, depending on how long your truck is, does ti have a 2 piece drive shaft and is it 4 wheel drive. So figure about $45 for the seal and about $125 for labor.

if its like any dif it takes about an hour to replace