Reputable breeders sell breeder birds and not culls, if a breeder is selling the worst from the hatching (other then at auctions or as layers) then they are not good breeders IMO
That is a very loaded question. I seen one of the dumpiest looking jubilee orp go for 150.00 that I would not pay 10.00 for and seen great english birds given to me.
Personally I prefer eggs you may pay the same for 6 eggs you would pay for a bird but with eggs you have a chance at getting a good bird. With buying a bird I assure you it is the worst from the hatching...usually. IMO Chicks are a gamble also because of shipping and possible disease.