I guess that shop has never done diff work before??
Some pretty basic mistakes.
Bart, the amount of work depends on if you have complete differentials, or just gear sets.
And then, if you have complete diffs, are you willing to install them without changing the bearings.
As soon as you disturb the bearings and gear sets, you have to go through the whole rigamoral of setting up the mesh and backlash, and then setting the preload on the pinion bearings.
Easy to do when you know what you are doing, but rocket science if you don't.
PK