The concept of "purchase", or monetary transaction may not exist in the future dystopian world.

For people who live low lives, barter is going to be good enough. For overlords, they can also barter with each other, because who cares about money when you can grab real stuffs? There are a handful of skilled human servants who serve the overlords, but they are not numerous enough for a mature market -- their overlords will provide them with whatever they need anyway.

I have long realized that monetary transaction is just one abstraction for the elites to buy human resources and nature resources. Some currency, like the USD, also serves as "entry ticket" for some transactions (like you cannot purchase X in bulk without USD).