I wouldn't pay for such. It's the most exploitative thing in the convention circuit, IMHO.
I've got photos of me back in my teens with a bunch of actors, from before they started doing these pay-for-them things.
Wouldn't pay more than $10-20 for such a thing, IMHO.
It's just... it's wrong to charge so much for such.
I can see a minimal fee like I said above, but nothing beyond it. More than a $20 and it's really silly, when you think about it, to pay such for a photo of you with someone.
I dunno, that's me. *shrug*