That's the cost of chicks. For example the BCM's if you get a straight run (unsexed) they are $11.15 each, but if you want all females (sexed chicks) then you would add $2.30 per chick bringing the cost for each chick to $13.45.
It costs more to order chicks that have been sexed since they require more handling at the hatchery. There's a select few of employees that are trained for sexing.
I would "assume" the difference in the "sexing fee" is breed based and it may also be based on the source (hatchery) that the bird comes from.
You are using My Pet Chicken as your example - they are not a hatchery, they are a third party that sources breeds from various hatcheries so that fee may be dependent on what each hatchery charges for sexing.
Make sense?