According to the State Library of Kansas website Kansans downloaded 230,944 audiobooks and 27,032 ebooks in 2010. As of today SLK has 7757 audiobook and 2452 ebook titles available on Overdrive.
http://www.kslib.info/skyways-root/K...20digest11.pdf
I cannot imagine what Overdrive will charge large circulating libraries in the next few years.