The supplement industry news website Stack3d reports that Costco has expanded its Kirkland Signature brand into energy drinks, a move likely to catch the attention of anyone who consumes these amped-up drinks throughout the day, given the sub-$1-per-can price point. Energy drink stocks are trading lower mid-session on Tuesday, though it is unclear whether this is due to Kirkland’s entry into the space. “Kirkland Signature Sparkling Energy Drink is now showing up in Costco warehouses in a variety pack of 24 cans, with eight cans each of three different flavors: Tropical, Peach, and Orange,” Stack3d wrote in a note on Monday afternoon. Stack3d noted that each of these Kirkland cans includes “some taurine, glucuronolactone, and, of course, caffeine at 200mg, similar to Ghost and Celsius.” A 24-pack of energy drinks retails for $16.99 at Costco. The math works out to about 70 cents per can, a massive savings that will really add up for the daily user who spends roughly $2 to $3, if not more, per can. Based on current prices, Celsius 12-oz. singles …