Castrol TWS synthetic oil - BMW - Dude - {P}

I understand BMW are recommending Castrol TWS (10W-60) for use in the M3 & M5`s, because of excessive oil consumption using the ultra thin SLX (0W-30).

Have Googled a search without much success and was wondering if any B.R`s know what sort of price this oil retails in comparison to SLX.??

Value my car