BMW is charging $18.23/liter? Wow!

Unlike Dexron III, GM is very tightly controlling the Dexron VI formulations and is not allowing much variance from one to the next. Dexron is GM's trademark, and to get a license to use the Dexron VI mark from GM, you have to comply to their spec exactly. Therefore, there are not going to be big differences between the different brands of DexVI and BMW cannot claim that theirs is special. You can easily get almost any other DexVI for $6/liter or so.