Walmart has M1 in a 5 QT jug for $23. All different weights, and even SD_GR's favorite "Truck and 4x4" 5w40. I picked up a jug of 5w30
Around here m1 is around $6.50 at autozone, Kragen, etc.
5 x $6.50=$32.50
So its an avg savings of about $9 on an oil change