I actually just sold the remaining M1 15w50 stock. I hadn't kept up with prices and had it listed accordingly but Walmart has changed. They now list 1 jug for $31.97 which is outrageous but online you get get the multipacks where they are only $24.97 each. I sold mine for $20 each and gave one free because they took all of it, had I checked the current price I wouldn't have done that. I had it listed for a few months and just now sold it. I still came out well ahead though and purchased it during those special deals from a few yrs ago if anyone remembers.
I checked others on there, SOPUS is the worst offender. Pennzoil Platinum is $35.97 and Quaker State Full Synthetic is $29.97. Castrol is currently on "rollback" but was at least priced normally, even Valvoline is higher.