In my experience, the CPM model does not pay as much as the CPC and the CPA. However, if you are planning to use the CPM to achieve inner ad process inside your website it is feasible but it would require a large amount of impressions. This would lead you to pay a lot for a small traffic. My advice to you is to switch the model or should you remain in this one, you can go for Affiliates other than Google such as Kimia, Mobusi basically the affiliate marketing big guys. If you have any further questions, I'd be happy to answer them over a phone call.