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).
One thing to remember is that publisher revenue is net Google's monetization cut. Publisher's see just 68% of ad revenue sold on their site. So $150 is really $220.58 in gross, which is significantly higher.
Another point to remember is that typically publishers only sell to Google AdSense their unsold (so-called "non-guaranteed") inventory. Typically you take this money because it's better than nothing, and because you couldn't sell this inventory yourself. Usually this non-guaranteed inventory has a lower value then the stuff you'd sell yourself.
There's a lot of reference-style material on news sites, and the CTRs on that are not bad. Just look at Wirecutter and its affiliate model.
That said, industry average for news display ads is about 0.05%... 1 click per 2,000 impressions. No bueno. Say 3m impression get 1.5k clicks, that's $0.33 CPC net or about $0.49 CPC gross.
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).