We had 34 trucks at one time and Walmart could sell us Rotella cheaper than our jobber.
You can buy both at Walmart. I would price it there.
It seems to me that Walmart has two price books.
One price in places where there's no competition, and lower pricing in more competitive markets.
I noticed this while stocking up on Shell Synthetic Gallons. Sometimes store would only have four and I needed 10. I would hit 2 or 3 stores the week before my oil change.