You should keep your Fedi instances small, and share their cost.
Fosstodon posted that their new hosting cost for their influx of users is at about k a month now. If the Eternal September pattern holds true, the cost will continue rising unless they stop signups. And because the new user base are web2.0 conditioned normies who believe paying for anything is out of the question, they won’t grasp that they either start sharing the cost, or surveillance capitalism and advertising are not far behind. the Fediverse will begin to centralize around large instances which can afford the infrastructure. New “standards of federation” will emerge. Activity Pub development will start to be dominated by institutions and then corporations. Smaller instances will be “defederated for safety”. Who knows.. Google may even start to “contribute” to Fedi development.
Or, you can keep your instances small, and share the cost.