What is expensive about $15 per 5 qt jug of synthetic? Yes I bought two boxes of it for the 24 or 22 don't remember if I got the sale, probably. WM has all kinds of oil at prices lower than before, and some higher than before, just like always it goes. Edge for $20-21, it used to be more. That's still 40-42 compared to Costco 30. Costco at 30 with no rebate is a heck of a good price.
It is the stores making the prices. If they can get more they try, if not they put it on sale. It's not like they follow what their cost is and are good samaritans about lowering prices for your benefit.