The cost of the Railroad Track isn't included in the price of the station/platform likely because they intend, when fully working, that you can snap it onto already existing tracks. You'll notice the extra items are the 2 Steel Pipes & 2 Steel Beams. This is the same behaviour as when you build a conveyor belt, if you link it between 2 Stacker poles or buildings the cost of the belt remains as in the builder menu but if you take it from a building/pole directly to the ground the price increases to include the cost of the conveyor pole to support it.