7 Things You Should NEVER Buy at Costco, According to a Shopping Expert By Gina Zakaria Costco can be an amazing savings tool in your arsenal. But you may be putting items in your cart that are costing you much more than you think. As a frugal living and budget blogger at The Frugal Convert, my mission is to find the lowest prices possible for the most common staple items so you save money on your grocery bill.