My understanding is that all of these custom runs are quite small compared with long standing previous tradition. Sometimes as few as 25. The reason they can be made at all is that the tooling is already there and decoration has become much less expensive per loco. The economies of scale (large volumes) aren't there, but you are dealing with sunk tooling costs, each additional locomotive doesn't cost that much to produce in terms of materials and labor. Since these are hand assembled in most cases, labor is a large component of the cost, after tooling, I'd guess. Materials probably come after that, and if you are getting a much more expensive motor and drive train, that likely adds to the differences as mentioned above.