That's a tough one... I got my first spam reply "thank me later" on Nostr today. I can see the value of paid relays and I'm considering running a one-time-fee relay myself.

In principle I'd be willing to pay a fee per post (maybe around 10 sats?) but in practice I wonder whether I'd find myself thinking twice about replying to people or posting in general. Not because it's expensive but because ANY fee puts in place a psychological barrier...