More affluent people would be charged more for the exact same box of crackers.

Or less, because they buy more stuff, and luring them into your store, especially for repeat visits, is worth it.

This is how it works today, just not to this level of granularity. Poor people can't buy the value size because they don't have the cash flow. Costco customers save a lot of money -- but they have big enough houses to store the large sizes.

It's really expensive to be poor.