I left my BAA IT role nearly two years ago, so some of what I say may now be out of date.
The BAA is a very low user of Zoom. We rarely use it to broadcast the main meetings, but some Sections use it for online meetings. Most of our main meetings are streamed direct to YouTube. Depending on what you are trying to achieve, YouTube could be a cheaper option as it is free.
Zoom also offer a non-profit license that may be worth exploring for your society.
As mentioned by James, there are others options too. As well as Microsoft Teams and YouTube, Google Meet was excellent the last time I used it, and there are many other virtual meeting providers.
