Walmart offers the STP High Milage Fuel Injector and Carburetor Treatment 5.25-oz. Bottle 2-Pack for $3.18. Opt for in-store pickup to avoid the $5.99 shipping fee. That's tied with our mention from a week ago and the lowest price we could find now by $8. Intended for vehicles with over 75,000 miles, each bottle treats up to 21 gallons.