Ad blocking cost German publisher ProSiebenSat.1 €9.2m in ad revenues in 2014

"By some estimates, more than 200m people worldwide are now regular users of ad-blocking programs (Adobe, PageFair). Eyeo, the maker of Adblock Plus, the most widely used such software, says it has been downloaded more than 400m times. Until fairly recently, ads were mostly being blocked on desktop and laptop computers but now people are installing the software on their mobile devices, which are expected to account for a growing share of their time online.
[...]
Not many publishers put a figure on their losses from ad-blocking, but ProSiebenSat.1, a German media group, has said that in 2014 the practice cost it €9.2m ($10.4m)—about a fifth of its web revenues. Publishers with a male, technophile audience are worst hit, says Sean Blanchfield of PageFair, an Irish startup that helps publishers quantify and manage ad-blocking. At some online video-game sites more than half of ads get blocked."

Source:  The Economist, 6th June 2015