Walmart offers the Valvoline SynPower SAE 5W-30 Full Synthetic Motor Oil 5-Quart Bottle, model no. 611291, for $18.98. (Amazon charges the same with free shipping exclusively for Prime members.) Opt for in-store pickup to dodge the $5.97 shipping charge. That's the lowest price we could find by $17. It purports to offer high temperature, sludge, and varnish protection.