7 1/4 to 8 3/4 rear end swap info needed
Like I said typically an 8 3/4 A body rear complete with open diff would run you around the 800 mark not rebuilt, at least around here anyway. If you look at some of the prices for just the center sections sold on here, they can vary from 350 to 550 for a suregrip center. So doing the math I would say a complete rear, with suregrip, rebuilt, is worth the 1200.
That's been my experience and just my opinion. Some will say they can find them cheaper, if you can, better yet. I would also try and find one with good drums, as they can be hard to find. Large bolt pattern is a huge plus.
IF you find one rebuilt, ask for some documentation as to parts etc just for peace of mind. Also when you check it out, spin one drum in a forward rotation and make sure the other side turns in the same direction, that will tell you if it's a suregrip or not, at least from an honest seller.