How much could I get for Heath Ledger's autograph?

When the Dark Knight was being filmed my friend's brother managed to get me Heath Ledger's autograph on my copy of Brokeback Mountain. I also have Christian Bale's, Michael Caine's and Christopher Nolan's on the Prestige and Christopher Nolan's on Memento. How much do you think I could get for those if I sold them on E-Bay or something?