The CPC values are provided by the Google AdWords keyword tool and they are, unfortunately, quite inaccurate. They should be treated as rough estimates more than anything. One of the issues is that there are actually many different things that factor into the cost per click on the advertiser's side, such as the quality score of their landing page and the position that they are bidding on.

You could use the CPC as an indicator of one out of three possible states:

Any CPC value lower than $1 = no one's paying for this. 

Any CPC value over $1 = there's probably some money in this.

Very high CPC values of $5+ = there's definitely some money in this.