I think that the amount of ball pythons that have been/are being raised successfully on an all-rodent diet shows that they do quite well on a non-varied diet. Check with any of the larger ball breeders, and I think you'll find they all feed all-rodent diets. It's what works.
If you feel that your snake will benefit from feeding chicks, or different types of rodents, that's your choice. But if your snake decides to eat only chicks at some point(ball pythons being known for doing silly things like preferring a certain color mouse) you'll have to go out of your way to find chicks. Then they might not be cheaper.
I feed rats. Simple, easy, and the snakes eat 'em.
Wolfy