maybe not exactely what you're looking for (not open source and not non profit) but there is some solutions out there like this one: https://elest.io/
Lets Encrypt serves nearly 192M websites with 13 full time staff and an annual budget of approximately $3.35M, for example.
I'm not worried about who owns my data, but I do want to have a stable identity. The first Mastodon server I signed up with mysteriously disappeared after a couple of weeks, so I decided I was better off paying a small monthly fee to put it on my own domain.