All in all, well under $50k in licensing costs. Basically a rounding error, if you compare to something like AWS billing for a website of the same scale.
I wish. Microsoft SQL Server Enterprise Edition (which is required if you want to use over 128GB RAM for caching data, or servers with over 24 cores) costs approx $7,000 per CPU core.
Our websocket process currently has ~500k concurrent connections across 9 web servers.
Nick has some information on his blog (https://nickcraver.com/blog/2016/02/17/stack-overflow-the-ar...) although it’s a little outdated - we no longer use Netgain, we use the .NET Core websockets bits instead.