There is a version of Costco membership that most members are using. And there is a version that a small, informed subset of members are using — the one that involves knowing not just where to find the best prices, but when. The when is where most of the real money is at Costco. Patio furniture bought in March costs 40 to 50 percent more than patio furniture bought in August. Holiday decor bought in December costs 50 to 75 percent more than the same items bought in January. S