If you are "not" near a large Airline Hub, or an airport that connects to the Hub, the vendor normally uses, shipping cost will be higher.
Its all about proximity.
When I lived in Milwaukee a Southwest Airlines Hub, I could get heavy fish boxes fairly inexpensively thru that airline, whereas a tiny box fro say, Seattle on another airline would cost the same.
Its also about the weight, a large fish like a semi adult gar, will cost an arm and a leg, compared to a bag of fry that only need a little water, so inevitably cost considerably less.
Also in the midwest, there is a service call Speedee delivery (which covered an area of about 5 states) that I could ship fish (within those states)for around $20, and they would pick them up at my door and deliver that same way.