If you want a service which indexes every post in the public network, including from folks you don't follow, that is just going to require resources. I think $200/month for a full-network index (as zepplin does) is very reasonable and approachable for organized groups without external funding. Many Mastodon instances cost more than that, and provide a must smaller scope of indexing.

If you want a small scaled down setup for just a small community, which still interoperates with the full network but doesn't have a complete network, there are setups like AppViewLite, which can run on, eg, an old laptop at home: https://github.com/alnkesq/AppViewLite

Personally, I don't think individualist self-hosting is a necessary or helpful goal for indexing the network. Most humans are not interested in spending the time or learning the skills to do this, even if it was as easy as setting up a self-hosted blog with RSS. I think small collectives (orgs, coops, communities, neighborhoods, companies, etc) exist and can fill this role.

Regardless, this is moving the discussion, which was about whether it was possible to decentralize each component the network, not whether it was pragmatic for individuals to self-host the whole thing.