I've found that the market is fickle. I bought extra chicks last season. All were breeds that would sell well. But, I could not sell them for enough money to even cover my costs. Folks want a great deal for far less than the value of the product. Then there's this: What do you do with the customer who wants to put a dozen birds in a 4 x 4 coop? Or the person who lost his flock to local predator, but still refuses to provide the security the birds need? Or the person who's dog ate their chickens, and their attitude is: well, I'll just buy more. Or the person who expects the birds to survive on cracked corn? I would refuse to sell to that person.
Breed birds for your own pleasure. Sell eggs or chicks or POL pullets and HOPE to recoup your expenses. Don't expect to earn extra money. You can't compete with the hatcheries!