Once you find a lower price, simply print out the product page (with the price visible) and use that to get a price-match at one of the stores below.
NOTE: If you’re going to try and get a Costco price-match at another store without buying a membership, your best bet is to use to check out their prices. While many retailers don’t consider “membership clubs” like Costco to be direct competitors, and thus won’t match their pricing, their are plenty who absolutely will and here they all are. Why drop $60 for an annual Costco membership when many popular retailers will happily price-match the warehouse club? Or maybe you’re already a Costco member, but when it comes to shopping for electronics, toys, and tools you have your favorite stores and would rather buy everything from a single place.