I bought a router from Costco once and a week later they mailed me a check for $20, explaining that they lowered the price on the item after I bought it. Like, who does that? They have an amazing return policy too. Costco is awesome. If you drive a lot, then just the gas savings alone will cover the cost of membership. If you do most of your shopping there then the executive membership rebate at the end of the year will cover the entire cost of membership plus some extra money.
Edit: oh, and they sell hearing aids and hearing aid batteries at cost, which can save people who are hard of hearing thousands of dollars. Literally thousands of dollars on a one time purchase. For example, they have the top of the line Rexton hearing aids for $1499. Those cost $6,500 at any normal audiologist office.