There's also the time cost and, in the case of Costco, membership cost. Plus the general lack of knowledge of all of the above. With $100 perhaps I could walk

There's also the time cost and, in the case of Costco, membership cost. Plus the general lack of knowledge of all of the above. With $100 perhaps I could walk into Costco and get huge quantities of maybe 1/4 of what I need in a given week, and because I bought it at Costco instead of Dollar Tree those items will last me two months instead of a week. But now I have to go to Dollar Tree anyway and that's hard because I work 6 days a week and Costco is really far away because I live in a rural town where even a Walmart is at least 20 minutes away. It's of course smarter to take the 20 minute drive to Walmart and save even there, but if I'm rural and uneducated I probably don't know that and assume that the per unit price at Dollar Tree is roughly the same as Walmart.