Walmart sells the 5 quart jugs for $22.88 for the regular mobil 1 formula and $25.47 for the high mileage and extended performance formulas. After the rebates, they cost like $10 or $12 each.
That's actually pretty common. Because they know they sell it cheaper than everybody else.
I've never had an issue with them not honoring the rebate. YMMV