This just seems like punishing the poor, very much like fines for speeding. "Rich" people get the freedom to do and say what they wish, but the poor must sit still and only convey favorable opinions.
It's $5, not $500. Anybody using an account long-term will experience more cost from having it deleted than from paying that amount for a new one.
The reason it works is that a poor person gets to amortize that $5 over the life of the account, typically ten years or more, which makes it a negligible amount even for someone making minimum wage. Whereas the spammer gets banned and needs a new account every 90 seconds.
And if the problem is that your mods are imposing censorship on disadvantaged people, you don't want something that makes that sort of "moderation" effective. But that's a different problem. Maybe try not having such a small number of large platforms so it's easier for people to abandon the ones doing such things.