I called the dealer and their first quote was for a rebuilt rear diff, all new bearings and new backing plates. Not sure what the backing plates are though. Total including parts, labour, shop fees etc was going to be $1080. For rebuilding the existing diff was going to cost $700 in labour, plus parts. The tech said that this would be the riskier option because its impossible to say what condition the rest of the rear end is in.
Now here I'm paying about $95/hr for labour so your prices will likely be a little lower. I'm going to try to get other opinions around town and hope I can get a better price.