The supplement category is where Costco's institutional pricing generates some of its most quietly significant member savings — because the same active ingredient, at the same potency, in the same dosage form, can cost 60 to 80 percent more at GNC, Vitamin Shoppe, or a health food store than it costs at Costco. And unlike the grocery categories where the Kirkland Signature quality story involves some quality trade-off for price, the Kirkland Signature supplement line operates