OK, I’m only saying this because I’m not allowed to have sites in this industry for two years, but the broadest and deepest market is colleges/universities/education.
You should be looking at an average $20 per lead. In terms of search marketing, it’s huge – tens of thousands of search terms and 10-15% conversions.
As I say, I’m no longer in this market ‘cos I just sold out for the big bucks, but it’s the easiest money you ever made online.