How do I make a user account system so each user has a proportion of the internet usage?

I want to set up a system over a few computers on a wireless/wired network, so that each user only gets a proportion of the internet download limit. Or they only get so much credit, when each mb costs like 3cents. What software or other thing would i need? Thanks.
How do I make a user account system so each user has a proportion of the internet usage?
You can do this with a high end router, or a proxy server, with specific software. Not all proxy server software will let you do that so research it first.
Reply:You'll need a pretty high-end router for something like that.