1998 Jeep Cherokee Rear End slipping and noises

I have a 1998 Grand Cherokee Laredo that has been making a Roaring noise (In the rear End) and it has slipped a few times recently. I think the rear end needs rebuilding. Does anyone know about what that should cost
or what my most inexpensive way to get the problem fixed without me doing it of course (Because it needs to work).
Where would the best place (Not Dealership) to get this fixed and where is the place to buy Inexpensive parts. The Jeep is 2 wheel drive with automatic Transmission. I bought it new 11 years ago.