At DragonCon you don't have to buy a separate ticket for each celebrity, at least not in general, though they might have some of the really big names in a separate location away from the Walk of Fame. But for the most part, and I'm sure for Dean, he'll be in the Walk of Fame, so with a Con badge you can get in there and just wait in his line to meet him and get his autograph.
Also, you asked about pictures. Some guests allow you to take pictures with/of them at their table in the Walk of Fame (some charge extra for this and some don't), and there are also at least two professional photographers who will charge for pictures with certain guests. I looked and Dean is on one of those lists - he may still allow photos at his table, but I wouldn't count on it. You can find that information here -
Froggy\'s Photos .
