I've been to almost all of them - I missed the one in Atlantic City back in April.

Whether you get to talk to them or not depends a lot on circumstances.  For example, if they've got a huge line of people waiting for autographs, you may not be able to talk with them much.  Also, some of the "stars" are there *only* to separate you from your money.  They don't really care much about anything other than selling their dvds or photos.  I even recall one star (who I will not name) who prevented guys from taking candid pictures of her.  She had a security guard go up to guys and block their shots.  Of course, if you paid her $20 she was more than happy to let you take a picture... and at the time that was about 4 times any of the other stars were charging for photos.

On the other hand, there are some stars that love talking to their fans and will just talk and talk and talk even when there's a line - they figure (rightly so) that every guy in line is waiting for their opportunity to chat with her.  I've had some wonderful conversations with some of the stars at the expo, booked a few dates here and there, and made a few friends.  Some of the girls are real sweethearts.  They're not all mercenary bitches.

One warning: be careful about saying anything to any of the girls about escorting while on the show floor.  There are too many people around with big ears and bigger mouths.  It's possible if they know you and you're careful but for the most part, it's dangerous.  And some of the girls can get really bitchy about that.

I'm sure you're interested about costs so I'll answer that now: some of the girls will do photos with your camera for free.  Others will ask for anything from $5 up to $20 now.   I haven't met anyone there who won't take a picture with you with your camera.  Photos that they have available for autographing can run from about $10-$20.  

Hope this answers all your questions.