Consent isn’t something that’s bought or sold, ‘bought consent’ is literally coercion.

Compare and contrast two situations: one, where two people go “hey, we both like each other and are both horny, let’s do it tonight” and thus doing it to share intimacy/mutually satisfy their needs and another where a stranger goes “hey, let me fuck you and I’ll give you money so you can afford your future survival, or starve to death”, and it doesn’t have to be money but position of power or other type of coercion. Even if the other person in the second example agrees, it’s not because they freely “want to do it” (they might not even have a choice) but because of what they might receive after the act, one person using their position of power over another.

If it’s coercion, there can be no free consent. If there’s no consent, it’s rape (like the definition you dropped says). If the rape is sold for money, it’s merely commodified.