PS - IMO Buying an autograph is the very last step. Learning what to look for, what is real, what it should look like, how/where signed, when, with what, common inscriptions, the common forgeries and secretarials (if any) to avoid and so much more. How much should it cost? Look at the sellers other closed listings. If items worth hundreds or more are closing at Buy It Now with no bidders or 1 bidder there is a problem. Knowing more than your seller is a GREAT help.
One other thing - seller trust must be earned - not given until proven otherwise.