Not a large fee. Just something like the local equivalent of $10 USD.
The deposit sits in escrow during a probationary period while the new account holder has to prove they’re here with good intentions. If the account starts spamming, advertising, trolling, or plugging their slop-coded garbage, they get banned and forfeit the deposit to the instance they signed up with. If they interact in good faith for the “probationary” period without showing signs of being an LLM bot / gaming the system / “karma farming”, the deposit gets refunded in full and they exit the probationary period.
If they don’t interact enough to prove their intentions here a good, the deposit still gets refunded in full but the account gets banned.
This would virtually eliminate drive-by spam and trolls while also funding instances and encouraging positive engagement.
Is it feasible? Probably not. Is this an idea likely to be popular? Nope, otherwise I wouldn’t be posting it here. Do I think this is a good idea? Yep.
Something Awful forums did something kind of like this. Creating an account was $10. If you got banned, you were allowed to create a new account. It was kind of like a swear jar. People there tended to be a bit more educated (still stupid, just educated) and have jobs so the post quality was (usually) a fair bit better than places like 4 chan.
A swear jar where “mangosteen” was a swear lol
But, SomethingAwful was actually exclusively accesible to those who paid that $10.
The Fediverse?
If you are actually federated to any other instance… they don’t need to pay the toll.
You could set up a private, insular instance, but that’s the only way this even possibly makes sense.