mb
Lifer
Depends on the game, total # of players available, and # of players using the service. Can be hundreds a month (and into the thousands) depending on the bandwidth usage, and the more games and players the more machines you need. Once the game popularity dies down (like these old sports games) you still have to pay to keep them running.How much do "game hosting servers" cost?
Again I don't know for sure, but I'd imagine an authentication server can be run on one machine without using much bandwidth so long as you don't have tons of people trying to authenticate all at once (like when a popular game is unlocked on Steam).