How much, did you ask? About 1 penny per Gigabyte Download. Add another 7 cents for the cost of the line (maintenance) and you have a stellar 8 Cents a gigabyte, or $28.00 a month if you used every last one of the 350 Gigabyte cap.
Link: http://www.calgaryherald.com/business/Internet+services+marked+study+says/4547037/story.html
Mind you, most people use far, far less and probably weigh in at around 5-10 GB a month. So their profits? Well, again, the salaries say it all.