I found this deal for Red Line fuel system cleaner 22% off at amazon for a 4 pack. Comes out roughly to $12.49 per bottle. The other packs with more or less bottles are not as cheap per unit. Great deal considering most local and online vendors charge $15.99-17.99 a single bottle.
https://www.amazon.com/Red-Line-60103-4PK-Complete-Cleaner/dp/B00NQB6O0A?th=1
https://www.amazon.com/Red-Line-60103-4PK-Complete-Cleaner/dp/B00NQB6O0A?th=1