Comment by CaptainMarvel

It's free. It has apps for iOS and Android and you can also phone in. I've never used it for such large meetings, but apparently it handles 100+ people fine [0], and they have a blog post about scaling [1].

[0]: https://www.callstats.io/blog/2017/10/09/jitsi-atlassian-web...

[1]: https://jitsi.org/jitsi-videobridge-performance-evaluation/