Well, the puzzle goes for $15 - 30 on eBay unsigned.  I got my copy in decent shape for the low end of that.  I have seen a few sellers trying to get around 50 for it, but seems bit much.  Now, with the signature, that is the wildcard.  I would add at least $30-40 for the signature alone.  (Typical price I have seen celebrities charging for autographs unless they are really big time stars, then they can charge more).  I wouldnt hesitate to pay $40 to $50 for it, doubtful he signed that many of these.  The bigger issue will be shipping, depending on where it ships from since a larger item, though thankfully lightweight.  Many buyers do factor that into bids/offers.