A hidden economy would leave fingerprints the stories only sketch

The novels show a currency, a bank with a grievance, a shopping street, and families who are poor inside a magical society. They do not show a price index. That absence is an invitation, not a missing chapter you can cite.

If a hidden population buys school trunks every August, somebody tans leather, grows food, and decides what a galleon buys in muggle pounds. Fan essays that invent those numbers are doing economics, not transcription. The useful question is which pressures the text actually bothers to dramatize: inherited vaults, working poverty, and a bank staff that does not trust wizard history.

This note guesses that the alley is the visible tip of a service class the castle depends on and rarely names. It does not claim the author confirmed a model.

The stories are school stories. A price list would not make the train more scarlet. Silence about exchange rates can be focus, not a riddle with a solution in a later interview.