Amazon offers the Keurig Coffee Maker Descaling Solution 14-oz. for $7.99. Order via Subscribe & Save to drop it to $7.59. With free shipping, that's the lowest price we could find by $2, excluding the mention below. It's compatible with all Keurig series brewers.

A close price: Walmart has it for $7.99 with free in-store pickup. Also, be sure to cancel Subscribe & Save at Amazon after your item ships to avoid being billed for future shipments.