Where to, if I may ask? I have some small projects I'm trying to get away from SF, and the mailing lists are the hardest bit --- finding mailing list providers which support bulk import isn't easy.

GroupServer [1] is very nice, a hybrid between an online forum interface and a fully-functional mailing list. The installation and configuration process is fairly involved, though, but turnkey hosting is available through OnlineGroups.net [2], from $2/month [3].

[1] http://groupserver.org

[2] https://onlinegroups.net/, https://onlinegroups.net/l/groupserver

[3] https://onlinegroups.net/pricing/

That looks fantastic.

Discourse is what we're currently looking at. They have very nice pricing options for both one-time-installs and continued hosting/support.

I looked at Discourse, and for the scale of my projects the pricing is unmanageable. Hosted by them it's $1000+ a year; hosted by me it's still $100+ a year ($200+ for the first year). Installing it and running it myself requires spinning up a moderately high-end docker instance, which I'm unwilling to do (not only does it cost money, but I've only just managed to stop running my own servers, and it's great).

Have a look at discoursehosting.com, they have been around for quite some time and they offer 3rd party discourse hosting for much lower price compared to the official discourse.org hosting.

Why don't you pick the one-time install ($100) on a server you already own? If your ML is low-traffic there's no reason it should cost you much more than a couple dollars a month.

They won't install it on my own server. The $100 one-time install fee installs it on a virtual server with Digital Ocean, which then costs $10 a month hosting.

I thought Discourse was a forum software.

It is, but it has a mailing list mode.