Ends 4/14 at 10PM PT. Tools.woot! has the 1-Gallon Meguiar's Hyper-Wash on sale for $19 with free shipping with Amazon Prime, otherwise $6. High 400:1 dilution ratio (mix 1 ounce per 5 gallons of water).

If you are using an ounce per wash, that's 128 car washes (or about 15 cents per wash).