Ya but you're a pro Stephen!
Klaas I finally found a definitive number for you. Not saying it's the RIGHT number, but it's a number.
The guys over at the 30 Day Challenge that are teaching newbies how to make just a little money for starters in their 1st 30 days are saying to find a niche with less than 30,000 competing in "quotes".
Check out this video - exactly the info you need!
Again these concepts are for newbies and just to start off so you can get a little success. Pros like Stephen (and yours truly) can target and dominate much more competitive phrases.