How much would it cost to go on the computer? And how long? Are league of legends download on the computers already?

League is already there! $15-$20 for PCs all day

It cost $15 to play on the PC for all of their opening hours per day. It will cost you $10 if you are a member. It will cost you only $5 if you are a memeber AND arrive at 9:00pm. Not sure if it will cost you $10 or not for non-members at 9:00pm. See localhost opening hours online. Yes, League of Legends is already downloaded on all PCs. :)