VDO may be the OEM for that car, I think they are for my old E34. I see Husker has the BMW regulator for $125 (assuming I picked the correct model you have), so $120 for the VDO unit seems about right.
My car ate all four regulators eventually, there is a plastic bushing that cracks and can't be replaced apart from the entire regulator. I once tried a cheapo unit from Rock Auto that didn't last long. Considering how difficult it can be to replace them I wouldn't cheap out but that's just me.