Mine is aluminum, and it was like $35 plus tax or so. It's stupid, but I use it a lot:
Jesse BMW OFW12 Oil Filter Socket
This socket fits ALL old and new BMW spin on oil filters. Use your spark plug wrench to spin filter off and on. This "cool tool" is created with a computerized 16 tool changer CNC. It is machined with 52 separate angles so one low cost oil filter wrench works on old and new bikes.
I just realized it's not a "socket" oops.