I know I'm a little late to the party but I did some research on this. AutoZone is still advertising Royal Purple Heavy Duty 10W40 for $4.99, ship to home only. Free ground shipping (3-5 business day delivery) and you get a $15 gift card for orders over $100.
I called Royal Purple and asked what the deal was with this price. What this Tech told me was late last year Royal Purple changed their formula because of an additive they can no longer acquire (EPA). Their guess for the reduced price AutoZone is offering is that they are clearing out stock. He told me that price is a killer deal and he had no idea AutoZone was selling it so low.
As soon as I hung up I placed my order for 48 qts (4 cases) with ground shipping. :dance: