In my opinion this is completely fine as the pricing is in the packaging anyway. The salad bar is using the cheese from a much larger bin, thus the pricing structure is different anyway. This is no different than buying food in bulk. If the person is willing to go out of their way to package it from the salad bar themselves, then so should the pricing be less. If the store feels this is unfair then they should simply post signs stating so and move on!
When Customers Figure Out New Ways To Game The System, Everyone Loses