Doable I think but not that scalable (i.e. users may be not money)
Discussion
Yeah, I mean you can set it at 20 sats, which is about 1/10 of a penny. Doesn't take much to stop the bots. And many you could do a thing where you add them to a whitelist after their first message if they aren't a spammer.
Yes. Nostr is so groundbreaking, the old rules may not work. So I don't know what will happen.