If we're talking about English translated manga here, let's take for example Berserk. In order to buy that complete manga in English, it would cost you maybe $300+ (if it were completely released, that is). A decent ereader will probably set you back around $300 and you would have a complete manga library at your disposal anywhere you went. The reason I don't buy manga is because I don't have to. I wish there was a free way to make my manga portable, but this is the cheapest solution I see.