As a data point, I run the most popular blog in a technical niche and on a total basis, run about $5-6 in display advertising (job ads come to more). E-mail, on the other hand, is a lot better.
The only ads I run in e-mail are text (since text converts better with my geeky audience and they hate images as it is). I'm not sure what mainstream e-mail people do but images seem to be a lot more common there. If someone's paying $275 CPM to Thrillist for an ad - http://www.businessinsider.com/what-a-275-cpm-ad-looks-like-... - then I hope they're getting the full value on that ;-)