I make $1 for every 6 clicks from Adsense and $1 for every 11 clicks from Chitika - I get around 12 to 15 clicks on an average together from both
more like 68% for PREMIUM ADVERTISER, little guys like us receiving 33% if lucky, majority is 10%-15% percent per click. Do'nt forget, google is big company and needs to make more money to support and runs itself.
Try to check the location of the visitors who clicked on ur ads. The CPC + location finally decides the actual earning.
According to your expectation, you are trying to get $20~$50 eCPM, and this is not easy and i can say less people able to make it However, to achieve this, get more targeted traffic from high pay country. reduce those low quality traffic and study on the good pay keyword will helps