A New York Times writer named Ron Lieber recently did a comparison between Costco and Amazon on a basket of common household items such as diapers, laundry detergent, razor blades, batteries, and more. According to his experiment, purchasing the items at Costco cost $208, while purchasing the same items in the same quantities through Amazon cost $251. The difference can mostly be attributed to shipping charges, particularly for heavy items such as laundry soap.
Interestingly, Lieber points out that trips to Costco can end up costing more anyway because you will be tempted to make more impulse purchases when you’re at a physical store versus shopping online. That makes sense, and then when you add in the gas and time you spend driving to and from Costco, walking through the mammoth warehouse to pick up your items, and then standing in line, the difference between the two stores shrinks a bit more.
I personally prefer shopping online, and know that I have to pay for the convenience. But honestly, I cannot stand pushing through the crowds that are always, ALWAYS at Costco.