The server communication itself? Spectrum or Magic Transit. Spectrum is really expensive, and outside of Enterprise would only supported Minecraft (and at $1/gb), and Magic Transit is fully Enterprise whole network protection
It can sometimes break websites if they depend on a certain ordering and is more build for the "old web" where you had tons of scripts from random stuff which all tried to be loading at the start
Sure, the recommendation eitherway though is probably going to be disable it. It causes problems and is build for the old web/you probably won't benefit from it, not even CF recommends it any more in their new speed stuff
Cloudflare cannot mitigate raw TCP/UDP (which is what game servers use) without the optional Spectrum addon, which as Chaika has said is only for Minecraft and is very very expensive outside of an Enterprise contract.
Unfortunately we can't really give pricing details because it's very much specific to a contract. But yes, estimate at least a couple thousand dollars a month.