$ 11.72 when you checkout via Subscribe & Save (or less w/ 5+ subscriptions). Well reviewed w/ 4.4 out of 5 stars by over 28,000 Amazon customers. Lowest price according to a decade of tracking on CCC.

Also available, the 10-20 Gallon, 100 GPH [amazon.com] for $ 8.84 (temporarily out of stock buy may still be purchased).