Wait till u see how much Mark Hamil charges. He command over USD100 for an autograph. That's cos other than the fact he's Luke Skywalker, Mark Hamil don't sign autographs over the internet or through fan mails. Only at events and he don't attend much conventions except the big ones.
Harrison Ford charges even more cos he's the most famous among them, even till today. Even if you are willing to pay, Harrison Ford don't sign over the internet, fan mails and he don't even attend conventions. Only once in a blue moon do you get a chance to get his autograph.