If nothing else, you could open with just a Patreon or something. Basically as a way of outsourcing the "subscription revenue" implementation until such time as something direct yourself makes sense.
https://www.marginalia.nu/marginalia-search/supporting/patre...
https://www.marginalia.nu/marginalia-search/supporting/buyme...
(the text of the links is correct though)
A book, software, something. I can't quite expense patreon and others may have a similar issue. (Useful "free SaaS" where all there is is the cup of coffee button makes me sad).
My buyer won't even blink if I say that I need a $150 tool: I can just bill it to whatever project it's being used for as long as I get an invoice or a receipt or some kind of documentation. If I say that I found a free tool and I'd like to donate $10 to the author, no one will know how to do that.