I would guess £500 + + from a Dealer so not exactly dear if yours isn't working 😁
Check www.reaoem.com either search by Vin number then through the sections or by the Part number you have. If you aren't aware double click the part number and you should get a list of alternates.
Then check the normal Auction sites but don't forget there is a healthy BMW Specialist dismantler network they may help
Dave