I don't mean to cast aspersions on the developers—I respect everybody's right to try to get paid for good work, and this looks like good work. I am just not convinced it's the right option for my specific needs.
Remember, self-hosted mobile push notifications already have a free community plan!
I can't say whether Zulip might be a fit for your needs. But you can always email our lovely sales/support team. https://zulip.com/help/self-hosted-billing#paid-plan-discoun... should give you a sense of our policies.
I'm not sure what you mean by this. I am looking for a replacement for Discord for my small community of friends, and before today I had never heard of Zulip and knew nothing about its pricing or policies or history.