If you've got a million views a month page for a keywordyou should be able to sell an indvidual ad for big money.
I run maintain a blog for a friend for whom one page ranks highly for a particular keyword gaining her about 100 thousand pv's a month. We sold an ad on that page for about £150 a month. Yes they over pay. But with a million page views you could easily make more.
They're not for any individual keyword, they're for an enormous range.
For one single keyword it would be worth selling ads direct, selling inventory for a large range of keywords direct is a major headache. That sounds like real work ;)
I run maintain a blog for a friend for whom one page ranks highly for a particular keyword gaining her about 100 thousand pv's a month. We sold an ad on that page for about £150 a month. Yes they over pay. But with a million page views you could easily make more.