Mastodon.social had revenue (donations) of 326K EUR and operating expenses of 127K EUR in 2022 against roughly 191K users [1]. They have paid moderators to manage the server, and by most measures it's a healthy place. This suggests that the free market cost of social media is 0.6 EUR/year. The price charged to consumers shouldn't be much higher than this.

WhatsApp before it was acquired also demanded an optional donation of 1 USD/year from each person.

That is what people will be willing to pay, and what social media should subsist on.

[1] Annual Report 2022 https://www.patreon.com/file?h=90246790&i=16020862