I totally agree with Darkoz, I recently bought one from Advanced Auto Parts, supposedly I was told by a BMW mechanic from a BMW Dealership that the Beck/Arnley from Advanced Auto Parts should be the same one. I bought it for only $40 and replaced it. My first problem with this was that the o-ring was too small, which caused a leak right after I installed it. So I took it out again and used the old o-ring. Now the problem is that the CEL is still on with the same code for the CPS.
Lesson here for me (even though everyone tells you to do it - OEM) : Don't cheap out on OEM parts, especially electrical parts... I'm $40 under and still back at square one...