Wikipedia
Just price
The just price is a theory of ethics in economics that attempts to set standards of fairness in transactions. With intellectual roots in ancient Greek philosophy, it was advanced by Thomas Aquinas based on an argument against usury, which in his time referred to the making of any rate of interest on loans. It gave rise to the contractual principle of laesio enormis.
Usage examples of "just price".
She always made a bargain for it, by holding up, as a statement of its just price, one finger less than the merchant held up, whatever his number might be.
Then suddenly as if he were tired of it all, he interrupted one of Jabis' more impassioned pleas for celestial understanding of his need for receiving a just price with a single sentence.