Lets break this down first. CPM (clicks per month) does not return any money. What you need is cpc (cost per click). Now with your cpc the amount earned each click is based on the keyword, the more competitive the keyword and your ctr (click through rate) the amount of money per click is decided. So if you target finance keyword you will get a lot of money compared to small puppies keyword. Network banner ads generally only return small amount of money and relies on people cpa (cost per action). It is my experience banner ads do not work whereas adsense does. My profile under adsense has more.