It's just a websocket server; if you wanted you could use Node.js/Flask/RubyOnRails/Etc to make a basic webserver to support websockets (via something like socket.io); plenty of tutorials exist on how to do this with your language of choice, then use a cloud service to host it. It would be yours, under your full control, and so long as you deploy it correctly, you'd have no problems with using a low power, cheap host for a good couple hundred plus clients.
I don't want to go into detail about how to do this, though - that might be a bit too tangential.
If you want a no-code solution, you're much more limited; please keep in mind that WebRTC is a peer-to-peer solution, which means that if security is a concern, I would avoid this. The same can be said for that signalling server Sircca is selling. But, if you have no need for a central database/server and you are not conveying any sensitive information, it can be a cheaper and lower-hassle solution.