It isn’t a very long piece, but there are some interesting nuggets in an article on Japan’s e-book market in The Japan Times:
“Although [a spokesperson for comic-viewing software developer Celsys Inc.] said more content is available for other generations, the main buyers of mobile phone ‘manga,’ which cost about ¥300 to ¥700 per book, are women in their 20s.”
So that’s about $3 to $7 a pop.