100% per core metric is an easy way to show multi-core utilisation, but sure can be confusing. 🤷♂️
As for wowza costs - we found that using wow a is by far the most expensive route, but they sure have good experience with large scale streaming. One of our customers has a solution built based on UNA and Jitsi/Jibri/Wowza stack for live events with stages and large audiences. We can refer you to them if interested.
Facebook wouldn’t charge you anything for such service but they’d data-mine their $75K worth and then some from all viewers, so one has to pick their poison.
With any luck we will have a cost effective solution for scalable live streaming soon, but one million viewers is on a different level of complexity unless you pass distribution over to a CDN or a rebroadcasting service of some kind. Then you’d have to look into audience management apart from the stream - messenger, authentication, firewalls, etc.