May I ask; on what experience do you base your observations?
I dont personally do taxidermy however I'm friends with a bunch of folks that do Imports, skipped this time around but we just ordered a crate from Canada were spending like 200-300 CAD for the crate for several whitetail deer, mule deer, pelts, coyotes etc.
A kudu Is a massive animal about 50" alone for the shoulder mounts, and a few extra inches needed for ears and the detached horn plate You'll need another 20" length to accommodate the Nyla on the other side.
So about 60" height, about 50" length and 40-ish" wide. (depending on pose picked for kudu)
If your only taking back the skull cap, horns, and skins the box you need is a fraction of the size like pitiful small the only requirement being Its more than 35" long to accommodate the detached kudu horns.
Overall the smaller the crate the cheaper is gonna be, weight does drastically increase price however large light boxes do as well (larger, less space for product so marked up quite a bit so airlines/exporters get there moneys worth)