2000 Ford Excursion Noise in rear end of vehicle

I took my vehicle to a local garage, the owner of the garage tested the vehicle and stated that it was the left rear outer wheel bearing. The repair would 2 and 1/2 hours labor to do both right and left outer wheel bearing, the bearings themselves and 90 weight differential lubricant. The cost would be $340.00. I asked about inner bearings and he said it was not the problem and that they were located by the rear gears and had nothing to do with the problem.
I scheduled the repair, When I brought the vehicle back I told the owner that this repair needed to be right I could not afford to be exploring at a hit and miss approach.
After the repair was under way the garage mechanic informed the owner they needed inner bearings that were located right next to the outer wheel bearings (similar to the front wheel bearing configuration). The owner ordered them and informed me that his cost was another $80.00 + dollars but we would discus that at the end of the repair. After the repair was complete he had me take the vehicle for a drive and listing to the vehicle now. He did say the noise was gone and all I was hearing was a noise from the transfer case, but the noise was gone. So I took the car for a ride, there was absolutely no difference in the noise reduction. My vehicle is 2 wheel drive and has no transfer case (unless you call the differential the transfer case).
I am not sure where to go from here. I don't believe it is the tires due to I hear the whine (noise) all the way down to about 5 mph and then it clearly stops. I want to take care of this before it becomes a serious expensive breakdown and then I find myself on the side of the road at the mercy of another garage