Have you priced them through GM yet? Last time I checked just a Ring an Pinion from the GM dealership was north of 800$ and you are going to need 2 plus the shim kits, crush sleeve, pinion seal and nut at the least. Bearings should all be good still. As far as I know no one makes an aftermarket set for 9.76".
Edit. The front you can go aftermarket for around 350; it is same as previous years.