There are generally lots of BPs at any reptiles show, though with repticon it depends on the location. Usually on their website a list of vendors is posted and you can get an idea for what people are bringing.

When repticon came to Chicago there was a fair amount of everything. Not enormous because it was the first chicago repticon, but a decent selection of ball pythons.

As for prices, they are usually pretty consistant with prices on fauna or kingsnake. You will probably be able to find some breeder or well started males since they are sometimes a little harder to sell (especially single genes). Try and get a good deal! Usually you can talk the seller down a little bit for the older animals