>Things like financial products that charge higher interest rates to poorer people, or services that offer discounts for paying annually rather than monthly are great examples of this.

Exchange of future cash flows are not comparable to a one time exchange of goods or services due to the risk of default.

> And less direct things, like being able to drive to cheaper shops and buy in bulk, or being able to do preventative maintenance to avoid a cheap fix turning into an expensive one.

This is a good example, but the best example I can think of is having sufficient cash flow to be able to purchase a home in a higher socioeconomic neighborhood, because if you have kids, you are effectively paying almost nothing for a higher quality education since a lot of comes back to you in the form of equity and your child’s increased chances of financial stability.