I run a wireless ISP in Texas. The cost of buying upstream bandwidth doesn't change much, it in fact gets cheaper per Mb/s as the pipes get huge. The real cost change is in delivery. The backbone between towers, and especially in the access points all have to be increased to accommodate the additional load. In some instances, the access points cannot technologically accommodate the load yet.
The ISP model was designed on a over-subscription basis. In other words, you could have 10:1 users using a give bandwidth. With the advent of video like Netflix, this model is no longer going to be viable. We are seriously looking at having two different account types. One that will allow short video bursting, and one that will allow continuous video feeds. The latter account will cost much more than the former since it is what is driving the costs.