Unlike what a consumer might pay on AWS for traffic, large ISPs almost always typically pay for the size of circuits at the 95th percentile. They do NOT pay fo

Unlike what a consumer might pay on AWS for traffic, large ISPs almost always typically pay for the size of circuits at the 95th percentile. They do NOT pay for traffic per GB you use for circuits that fall below that peak circuit size - there is zero cost to any ISP for actual usage - it's peak usage. And, even then, peering makes pricing even more opaque, in which Tier-one providers negotiate mechanisms in which they agree to exchange traffic at zero cost, and just set up connections in meet-me rooms. Regardless, The parent is right - cost is not a function of data sent, but a function of peak circuit size for the ISP - so, if there is a period in which there is little usage of their network, the ISP can serve traffic at close to zero cost to themselves.