lol. Mechanic is on crack.
You can replace the bulb, ignitor and ballast independent of changing the assembly. The only reason to change the assembly is if it was damaged or AFS motors stopped working or something.
You can pick up an OEM-like aftermarket setup from TheRetrofitSource for $200ish give or take. You'll have to drop the bumper to remove the assembly, replace the parts and then re-assemle.
I did this on my '11 M56x. If your mechanic presses, find another one...or show him this post. Specifically me telling him to lay off the crack.
I believe the one I purchased was:
https://www.theretrofitsource.com/oe-re ... quantity=1
But if you're unsure, just call TRS and their customer service will take care of you. They are known for excellent CS.