Acording to this article the manga market had always been above 500 billion yen in Japan, until in 2006 it dropped into the 400 bilionyen range.
2006 Japanese Manga Market Drops Below 500 Billion Yen | ComiPress
That must have been what I was thinking of. I keep forgeting that the yen and the dollar have diffrent values.
So about how much would that be in dollars?