[hairyhandedfool]

The costs of building a single loco/unit are higher than the average cost of building two or even three locos because in order to build one loco requires a production line to be set up, which incures all the normal set up costs, however if there are two or three being built, the second and third (etc) will not suffer these initial costs. So if, say, twenty A1s were built the cost would be less per unit than a diesel loco