I'm not sure I see how this is a problem (or viable market). No income, volunteer resources - your best bet would be run it yourself (affordable dedicated servers, lots of free volunteer hours) and/or do it for/with others (like neocities.org is doing for web hosting).

Seems to be fewer such services now than a decade ago, but maybe something like: https://www.freelists.org/

The idea behind SaaS is that it's wildly more expensive (higher margins) because it frees up all those hours to making profit. So make a hundred spend fifty, versus make twenty spend ten on hosting. Or something along those lines.