how much should it cost to replace rear differential bearings in a 2006 Toyota m

Use this link to get an estimate from a good shop near you.https://repairpal.com/estimator Alex

Assuming this is a rear differential issue on a 4 wheel drive model - the rear differential is very expensive on this vehicle to overhaul. Have you changed your differential fluid ever? Again this is on a 4 wheel drive model only. However, do not forget the rear wheel bearings -- these could be causing your noise. This is a considerably less costly repair. Also, your rear tires could be making a "growing noise" if the tread pattern is worn in such a way to cause it. Troubleshooting overall is recommended.