I wish I was doing this show but it didn't work out for me this year, have yet to make it to the east coast Exxxotica.
Most girls charge $5-$10 for a photo with them. Some will do topless pics, they have to wear pasties over the nipples, but it's a fun thing nonetheless. Don't bear hug a girl or grab her really tight when taking the photo, this is creepy! Be polite and don't spend too much time talking to any one girl if there's a line of people at her booth, go back later when she isn't busy if you want to have a conversation. I doubt it's going to be like ComicCon with super long lines, etc. I've never seen a show like that, there might be a small line to see some of the more popular girls but nothing crazy.
Have fun! Stay awhile, some of the stuff that happens on the stage is pretty fun and entertaining!