I don’t know about Mastodon specifically, but for ActivityPub in general, I’m betting that efficient software, that’s easy to host in commodity hardware, and semi-shared resources (things like caching, file servers, outbound queues, and spam filtering) will make a dent, with the goal that you could host a private or sub-1000-user instance for < $10. @YurkshireLad @evanwolf