Note, though, that the only reason adding that to your muted words works is because this spam attack happens to use that domain for their profile pictures. If they change what domain they are using, the spam will be back. It's a temporary band-aid at best.

Also note that while this works on Amethyst, your muted words may not carry over to other clients. Amethyst encrypts the muted users and muted words when it adds them to your mute list, and not all clients support decrypting them, or muted words in general.

As far as "pay once" relays go, there's nostr.wine.