While admirable, a one time payment for a service you host is fair neither to you (what if I use it for 10 years) nor me (what if you shutdown tomorrow).
On the other hand, a one time fee for analytics I could deploy on my server a) makes financial sense for you and b) is an intriguing value proposition for me.
Have a look at https://once.com/
That's a beautiful site and a nice way to put it. But yes, you're right. While my server costs are low anough that just one user could cover months, it's still not sustainable. My plans is to move onto a "pay for what you use system" in the future.
But I have thought about making it self-hosted too. But there already is so many great products for that out there.
I wish there was a perfect way to do this. I despise subscriptions, I dislike pay as you go becasue it's too complicated, and finally, a one-time fee dosent really work when sold as a service as you said. But I guess these are the options for people not willing to self-host.
If you got any interesting reads on this topic please send em my way.