Billing and overhead eats into that revenue stream, lets make up a number and say its still $50-90 per month after expenses.
I don't disagree with the reasoning at all but it's the details that make all the difference. For example, this $50-90 is a real industry estimate or just some number pulled out of the air? This is the first "hard" number anyone has mentioned, and if reasonably accurate, then I'm surprised that the base cost is that high. However, I can see that a pay-in-full customer is marginally profitable at best if the relatively fixed monthly cost to keep the customer is so much.