Doesn't need to be 50k to prevent spam even 5k sats would probably be enough, a spammer could spend 50k or even more to spam in a single relay, but then all the bots would be banned after a short time and he would have to spend again. I would see a zap to reply as a way to prevent troll comments and I think it would be a cool feat, as long as we have options we will use them the best way.  

 I just threw out 50k cause that’s how much I thought nostr.wine was. I just checked and current price is 18,888. I’ve happily paid for nostr.wine, but I still read from free relays cause I know many people can’t afford to pay for nostr.wine and I still want to read their notes.