Not sure if at a noticeable level, but I keep wondering: aren't there costs that are directly proportional to the amount of data transferred? Flipping bits costs energy, both at the level of fundamental physics and (more importantly) at the level of engineering - all the electric and optical signals aren't free, and packet processing isn't either. E.g. I'd expect my power bill to be larger if my Raspberry Pi saturated the network by streaming /dev/urandom than it would be if it was sitting idle.
But aside that, I think that beyond the "we can charge you for data because you can", the per-data-transferred costs come from the overprovisioning ISPs do. The fraction of the advertised to actually supported bandwidth per user they can get away with is dependent on average amount of traffic users generate.