In September, Costco stocked Kirkland Signature Hydration in its warehouses: 40 sugar-free electrolyte stick packs at about 62 cents per serving, compared with roughly 83 cents for Liquid I.V. on Costco.com. It followed a Kirkland sparkling energy drink in March, at about 70 cents a can against roughly $1.55 for Celsius on the same shelf, and a Kirkland sports drink in June. Each launch targeted a functional category a branded leader had built and that Costco already stocked.