According to Bakery Cakes Prices, a Costco half-sheet cake will cost a meager $18.99, while a similar half-sheet from Sam's Club costs nearly twice as much at $39, BJ's half-sheet cakes are sold at $24, and Walmart sells theirs for $25. Furthermore, Costco's half-sheet cake provides 48 servings, meaning it should only cost about $.39 per person to feed almost 50 people.