It would also be interesting to see that as a rough $$$/user. It would be very interesting to see how much you need to be making from each user to cover hosting.
I did this migration recently and we're spending about 1.75 cents per user. We could do it for cheaper, but we've recently had some issues that were absolutely trivial to resolve with AWS, that would have been very difficult with our previous hosting provider.
This hits on something in the calculation that I feel is very hard to factor in, the cost of development time. Sure, there are plenty of ways to do these things cheaper on a hardware/software cost per user basis, but more often than not I've found that we can get changes out so much faster in AWS that you're easily saving thousands in developer time, which would seem to more than cover the extra cost to me.