You should be eligible for the 50% non-profit discount and could maybe even get it for free as an open source project: https://blog.discourse.org/2016/03/free-discourse-forum-host... (you don't exactly meet the threshold criteria yet but look at the top comment on that post).

It's 100% open source, there's a very nice Docker-based install. You can host it yourself on AWS or Digital Ocean for very little money.

Make a free Mailgun account and put your credentials into the Discourse installer and delivery is free up to 10,000 messages.