Well, expos (none that I have been to) have debit so you will need to bring cash. Any expo will do really. They usually vary in size and who is going to be there so it is up to you to research the breeders who will be at that particular expo. And prices vary depending on location and the breeder. The best way to find out an estimation on price is to look up what other breeders sell them for.
And just because I saw it, the scaleless ball python is super rare and so far I believe only two breeders in the US have actually produced one... They are pretty much priceless right now.