Well people pay large sums for prints of the Great Wave, of which many thousands were made and are still being made. (Of course the trick is to know which prints are the earliest ones)
I think there's a genuine reason for them to be worth more since they are closer to the original painting. There's a fantastic (and long) series on Youtube about this: https://www.youtube.com/watch?v=jAhiMCSvtCc
