How do you figure an ISP's bandwidth is a fixed cost? And there bandwidth transportation? And their electric costs which rise with usage? And their maintenance which rises with usage? And on and on. Rent, Leases and such are fixed costs. Not most other costs. Truck rolls increase with usage and do support costs. What is your business experience? -- Begin with the end in mind!
Their bandwidth costs (both hardware and transit) are based on peak Mbps not GBs per month. The equipment has to be running 24/7 and the electricity use difference between fully loaded and idle is really minuscule. A fiber/coax/etc will require the same maintenance no matter what the load is on that transport media. How do you figure the number of truck rolls increase with usage? The two greatest enemies of this type of equipment is time and exposure(both of which are essentially a fixed cost).
The ISP I speak of is a WISP, so the load on the radios does change the equation. The more use increases the more the customers have problems, more truck rolls. Usage does affect costs on the last mile infrastructure.
Don't get me wrong.......I don't support caps. Caps are merely the way the monopolies and duopolies, who control the middle mile infrastructure, discourage use. -- Begin with the end in mind!