Where video can start getting really expensive is, as you said, when you're centrally hosting/processing/streaming large amounts of it. For this use-case there's a good chance they don't end up touching the video streams themselves at all, which is really cool.
At cloud pricing you'll be paying $100/TB, but there are plenty of alternative providers that can give you great deals. Hetzner for instance charges $1/TB for their VPS solution.
You can also cut back on video detail depending on the project - you don't need to send 720p streams for something a bit more experimental or with other things happening.
Combined that's low enough that ads should easily cover the bandwidth.