Advance Auto Parts offers its Prime members the Chevron Techron 20-oz. Fuel System Cleaner, model no. 65740, for $6.50. Opt for in-store pickup to avoid the $9.99 shipping fee. (Amazon charges the same with free shipping for its Prime members.) That's tied with our mention from three weeks ago as the lowest total price we've seen. (It's also a current low by $14.) It's designed for carbureted or fuel-injected spark ignition engines.