3,000,000 for $150? That's criminal. How are you only getting 5 cents per thousand impressions? Are you getting really low quality traffic from far eastern countries or something? That's just extremely low even for Google. If your CTR is the problem, have you looked at placement optimization?

My recommendation is to sell the space directly on BuySellAds. At $1.00 CPM it would fly off the shelves, but you can get much more than that with a little patience (and provided that your visitors have at least some kind of quality).