The cheapest tier for Discourse is $50 a month for up to 100 users. https://www.discourse.org/pricing# With self hosting you can probably get that lower at the cost of your time getting it set up and making sure it's cheaper than the options they provide.

As much as we all collectively roll our eyes when we see Discord being used for community discussion, it makes sense from a maintainer's point of view.

Edit: Discourse has free options for creators

Eligibility Criteria

We know creators are not created equally, so we split the criteria or requirements to apply across the different creator groups.

• Software creators (GitHub, GitLab): 10+ contributors