Dude your problem is not ad networks, rather the monetizing strategy. Traffic is huge, but comes from 600 some search terms / phrases (very, very defragmented). I’d group all search term based on similarity. Find yourself some kick ass affiliate offers to go along with each visitor group. Serve the ads accordingly, instead of relying on Google welfare. Based on what I’ve tried and seen, you should be able to get $20/25 CPM at minimum.