>I've always wondered if it's intelligence agencies, criminal organizations, police organizations, or commercial endeavors that sell services to those three bodies that are paying that kind of money for zero days.

According to this article: 3rd party middlemen, small security firms and large defense contractors are the ones paying for 0-days. There's also has a nice price list for Chrome, IOS, etc.

http://www.forbes.com/sites/andygreenberg/2012/03/23/shoppin...