You may want to concentrate more on the content of your site. The reason why you are getting such low cpm is because the content of your site is only appealing to low-paying advertisers.
Work on incorporating higher-paying keywords into the content of your site.
There have been times when my cpm rate has reached $1000! Too bad I didn't know what keyword(s) triggered that becuae I would be using it all the time.
You like the rest of us have only 2 choices to earn more. 1) keep adding more pages, a lot of low earning pages add up. 2) Find a way to get your pages to show higher paying ads.
The more unique your pages are to other sites on the same subject the more visitors and higher paying ads you will get. New info not already on the web is always the best thing if you can get it.