A few years back I had to replace the windshield on the wife's 550. I can't remember the exact numbers but I believe insurance first said $800 and they gave me a list of shops they worked with that would do it for that price. I countered that the windshield was a structural part and that none of the shops could assure me that the glass they used was as strong as OEM. That got them to up it to $1200. Then I called local mobile installers, first one had no problem getting OEM glass but the cost of glass would be dealer parts counter price. Second guy had an account at the local dealership and his cost on the glass was significantly less. When all was said and done it cost me a little less than $300 out of pocket for OEM glass and a new rain sensor which is also a necessity as you cannot reapply them.

I know that wasn't exactly what you were asking but hopefully it helps some.