It does cost money to build the network in the first place, and funnily enough while the cost of cable is relatively small and the cost of digging it into the ground or hanging it off concrete trees doesn't change mich in relation to how many pairs are in use, it does cost a great big truckload of money to terminate the cable and send/receive data, and then route that data to someone else's network.
The costs you are indicating are similar to utilization fees. That is, if you utilize 100% of a cable's capacity, you pay 100% of the upkeep costs. Quotas are a simplistic form utilization charge, where you simply give the end user a proportion of the cable's capacity for a month at a set fee, then either charge penalty rates for over use (learn to budget, dumb end user) or shape to very low speed for the remainder of the billing cycle.
This is a model of billing that has been used in Australia successfully,with ISPs using the profits to expand their capacity. There will always be complainers, of course, but they will be the ones who assume that having a 20Mbps carrier means they should be able to download at 20Mbps all day, every day, for $20/month. Sorry mate, the world doesn't work like that.