Hardest part will be to find a second hand diff in good condition, which will save you a few dollars else you'll need to spend money reconditioning your existing one.
For me, a few quotes were ok to outrageous depending, but at the end I was lucky and got a good condition diff for $450 and the driveshaft issue done for $400... then you slap labour ontop plus some new bushes/mounts and you'll get your total.
Worth the fix though and I'd suggest you shop around to make sure you're getting the most, don't feel shy to ask as many questions as you can.
Good luck mate.