First, it's probably a "duh" issue, but please when you are outside the show with the snake, even inside a container, be discreet. Who knows what people would do confronted with a baby snake out in public. It might not be pretty.
Second, I was just at my first show- Daytona, and it seemed to me there were a lot a lot a lot of captive hatched babies with crazy prices on them. I'd say look for a baby that's nice and fat and healthy first and think about price next. $50 bucks is the range I would expect a captive born and bred normal to go for. Don't fall for really low or really high prices. Low price- you'll get a low quality animal- high price and you're paying for some stripe or pattern that isn't really worth extra cash. Try to research which breeders are the reliable ones there, ask questions-- are they farmed babies, have they had any parasite treatments, how much has the individual you like eaten-- don't be afraid to ask to see it eat first, and a responsible breeder should be able to tell you how much it has eaten, when it was born, etc.
I don't know how much you know about balls, from your first message it seems like you have done some research which is great. It just kind of made me sad to see all the little normal balls at Daytona in their little deli cups knowing that they were shipped from Africa instead of being raised by a breeder. Say what you will, but I support CBBs all the way for people who want a single or a couple balls as pets. It just feels a lot better to know where your baby comes from and then there is that extra assurance that it will be in good health. Anyway, sorry for the tirade. A rubbermaid with some holes drilled should be fine in a car ride for a couple hours. I'd maybe toss paper towels in there for some padding and hiding space. Keep the temp inside the car comfortable and keep the container out of the sun and it will be fun. Good luck!