If you're stuck and have to have it then biting the bullet and buying at the dealer's parts counter isn't always expensive relative to autoparts stores.
The BMW OE contract went back to Castrol, but it's the approval that's important more than the brand. X is better than Y, but your engine only demands the approval, not what brand.
Yep, I would love to get the Castrol from Walmart but its out of stock, is that about the only inexpensive LL17-FE oil? Rest seem about $45-$60/5qt?