1. A costing system, comprising: a costing model recording parent-child relationships between a plurality of stages of a production line, and at least one valuation type for each stage; and a costing engine to retrieve a first group of valuation type combinations corresponding to the parent stages of a target stage for stages from the costing model, combine a target valuation type corresponding to the target stage with valuation type combinations corresponding to the parent stages to generate a cost identification, and generate costing results accordingly.