My DS got lucky when he got his show birds from a breeder. He got his birds for $10 each because he belonged to 4-H.
He also went to a poultry show and bought a couple of D'Uccles, told the lady that he was buying them for 4-H and she gave him a $10 discount. So, he bought the pair for $15.
You just need to know where to look, and ask the seller if he will give you a discount. You don't need to spend a lot of money to get purebred chickens. They may not meet all of the APA standards, and that is why the breeder is selling for a lower price, but they do well at the fair.
My son's chickens all got blue ribbons, 1 got best of breed and 1 got best variety. They did not make grand champion or anything, but the experience and fun that my son had was all that mattered to him.
Now this year, we hatched a few chicks from his showbirds, so I think he wants to take them to fair, and some other poultry shows, if they meet the standards.