can you mine bitcoin with a PC?

what is the level of difference between them and what is the cost per hash, and time per hash, with current ASIC hardware?

what makes you think that the same arms race won't play out on nostr PoW antispam?

any conservative estimate is going to be wrong because it's probably based on the current size of the userbase and not on a future situation where half the internet has been driven off the mainstream social networks, that's hundreds of millions of users, and that's definitely a target for scammers