I saw a sketch somewhere diagramming a double bag with much more than air than water in a Styrofoam box within a shipping box with some blue ice. I did not keep a link because that was all the info. Might have been Google images as I lurk there a lot -- maybe not as I just went there and it didn't jump out at me. Try ~ ship OR shipping live fish site:.edu. ~

Not sure what OP means by "fancy shipping boxes and such." Sometimes the product designed to get a job done is in fact the best and most economical way to do it.