A baby will live longer. In every sense of buying a pet besides breeding a baby should be worth more then an adult in my opinion but even with other species its sometimes the case. The correlation would be an interesting one to look at to help determine the strength that breeders bring to the BP market though. It would be hard to gather the stats. I'm not saying it would reveal answers just would be interesting. With Chameleons people pay more for an adult because they have full color.
You can go to PETCO's website and they will show you all of the animals that they have the option to sell at their stores. They only offer a limited range of "fancy" ball pythons. They also have Green Tree Pythons and Red Tail Boas. I've been monitoring the petstores in my area for a while now and although a normal BP is priced at 90 dollars they often have sales where you can pick one up from 40-60 dollars. I've seen some pretty decent normals there and have debated asking to pop them in the store. The closest breeder to me will sell me females for about 40 now but they're obviously ones he doesn't want to breed as their usually very dark and don't have any real interesting characteristics.