Through 6/7, Family Dollar has the STP Son of a Gun! Tire Care (20 oz) and the STP Son of a Gun! Protectant (10 oz) on sale for just $2. You can use the $2/1 STP coupon from here to get these FREE!
Also, Walmart has the STP Fuel Injector and STP Carburetor Treatment priced at $1.87, so FREE after the $2/1 coupon!