Quick question about adsense cpc

(IMO) The main reason for the low CPC more often then not the word you're targeting isn't the one that got the click. And/Or you're looking at the search network CPC and being paid the display network CPC.

If your cpanel has Awstats or you're tracking the clicks with a service or software you can view the "keyword" that got the click. In Awstats scroll to the bottom of the page and you'll see the search term that got the click. I get the search term I'm targeting, but I also get a whole lot of weird searches that I haven't optimized my page for.

As for Google's keyword tool it shows the search network CPC, the display network is much lower (but higher percentage 68%). Unless you have a search box on your site you're using the display network. If you have an Adwords account you can view the Contextual Targeting Tool which the CPC will be much closer. Keep in mind it's only an estimate, and maybe it's not the top paying ad getting clicked on.

They do have Smart Pricing and sometimes the quality of the site/traffic will affect the CPC, but the traffic volume shouldn't matter.

Adsense is the most popular of those types of programs and pays the best, but they're quick to ban you for violating the TOS so read it carefully. They don't send any warnings to bring your site to compliance, no second chances. Chitika, Kontera, Adbrite offers similar programs, but Adsense is the best by far IMO