I think it's the prices... Depends on how much the basic heels cost you, though. But mod-podging (do you use mod-podge? Is it even called that in English?) pieces of paper to a shoe isn't that hard to do, though the idea is very original (I think). Also I cringed a bit at the idea of cutting up an actual book in order to make shoes :p
And also I think this is illegal, as you technically need a licence to produce items with Harry Potter, Star Wars, Assassin's creed etc. on them.