Through that, I got some links to services of interest that are membership-based:
A paid membership with Communick brings access to a bunch of services they provide.
https://wiki.social.coop/home.html
An optional paid membership with Social Cooperative makes one a stakeholder in their governance process.
Paid membership with Mastodon Green, in addition to access to the Mastodon instance, goes towards green hosting.
Advertising is like poison in the wider fediverse right now... which IMO means there is a big opportunity for an advertising-based server. Just be prepared for some of the larger peers to block you, so you have to make sure there is enough value on your local instance to draw a crowd.