That server cost seems very high, the same offering (2 vcpu, 4GB RAM) is €5.58/month at Hetzner for example.
https://github.com/capnmidnight/Calla/blob/master/Calla/doc/...
As for the server costs, I'm not going to use anything other than Azure. Most of the cost is bandwidth, but it's worth more to me to keep everything in one place and not have to worry about learning another PaaS system. From the other offerings I've seen, Azure is usually only more expensive at the most lowest of tiers. Once you start scaling up, the other vendors get just as expensive. So I'm fine with shelling out a few more bucks here and there to avoid having to use something else.
I built something similar as OP and chose a mesh solution for this reason even though it's inferior.
It appears that only big video chat companies like Zoom or Skype can afford to have a generous free tier, subsidized by their business offerings.
No one doing serious amounts of bandwidth pay outrageous big cloud prices. See: netflix.
What you got is a 200Mbps connection to your provider (and still that's probably a lie, it's probably shared before reaching their endpoint), afterward it's fully shared with every other customer... that's just how the internet is made, you can't have a dedicated 1 gbps to every single server, that just doesn't make sense.
Thing is, the higher the requirements, the more expensive it is to support, that's simple math... If you got 10 000 clients that download 1 gbps, you need 10 tbps, it's even worse if they are all on the same service, that connection won't support this, believe me.
The video is 320x240 and one stream is about 600 kbit/s and audio is another 30 kbit/s.
So yeah, that works fine for a few users that have maybe 5 mbit/s upstream.