according to some people a quite common exit is between 12 and 24 months[1] of the net profit. Considering his expenses (1700$) and sales (2500$), and initially ignoring the licensing fee, he had 800$ profit for six months, so let's round it to 150$/month, 3500$ is 24months of this profits. If we want to consider the single licensing fee, let's say he licenses once a year, it's 1500+1800 = 3300$/year, and so 3500 is a 12month evaluation. Still acceptable. 10-15k$ I think it was not acceptable (by the buyer of course) with this numbers, even thought he could have reduced significantly his EC2 expenses (and so having a much higher monthly profit)

[1] http://www.softwarebyrob.com/2012/02/28/the-inside-story-of-...