I've been looking at Liqui Moly. I don't know the price but their website and promotional material say "for BMW M application." It's the No.1 oil in Germany and I am sure it's TUV approved and also meets most OEM specifications. If it's cheap and given I hardly track the car, and change oil every 12 months/6k km, I will be going with LM from my next change.
E92 M3 2007 - ///PE with Test Pipes and BPM Stage II; CF Interior & Splitters; CIC with Connected Drive