Okay, here is a simple description. To buy a fish from Thailand directly it would cost a LOT of money! To save the individual money, the breeders will get a big box of 100+ bettas that they are selling to the US..That box will end up being about 150 dollars..But between all the bettas in there--it ends up being about 5-10 dollars a person depending on how many bettas are in the box and all that.
If you buy one betta, you add your average of 5 bucks to the shipping amount.
Then the betta makes it to america, and to your transhipper's home! The transhipper has certain things they have to deal with and they will ship the fish to you. Things like the heat pack, shipping, box, etc. will be charged to you so that your transhipper can afford keep shipping those hundreds of bettas each time!
So you pay for the fish--as well as your part in the transhipping. Then you pay for the actual shipping and handling fees in america! So the transhipper's fee is the only real extra thing added to buying a fish from Thailand, other than the fact that there are now two times the fish is shipped, risking a DOA at each place--though for a healthy fish, this is very rare!