They are not federating at the moment

I think the price is spread out across multiple generous people that generously host instances. I think it really depends on how much members there are. From what I heard my instance is 25 $ a month. Another instance I was in on Mastodon cost a few hundreds bucks to run. This is why it is good to help out your fellow admins. On the other hand, lemmy and other fediverse software are open source, so they don't really have to pay for developpers. Also the scope of what lemmy or Mastodon do is considerably smaller that Facebook, Twitter and the likes. Facebook isn't just a social media, it's a spying engine and an ad recommendation platform, Lemmy and mastodon are just social medias, so of course it costs less to do.

I join the biggest one