If you look at the ESM vs. KMP planes you will see there are somethings on the KMP planes which are not on the ESM planes, though they are the same airframe. For instance on the ESM vs. KMP T-28, they are the same size however the KMP plane features a hidden access for switches and air fill, as well as a functional (moveable) tail hook and cockpit. These items, from what I am told are not on the ESM model. This may explain the price differences.
I am just going by my research, and have not seen either in person, so correct me if I am wrong.
Thanks