Charges of X steel- Go by Tonnage or Go by Pieces of Drawings?

What is the reasonable rates for producing one tonne of structural steel shopdrawings? It is very much dependent on the individual firm. However wages for respective country will be taken into account in charging the production of shopdrawing. For example, country like Australia will charge a rate between AUD250 per tonnage to AUD500 per tonnage.

Country such as China will charge half of the Australian's rates. Some companies do charge according to the pieces of structural steel drawings to be produced. So, which one is reasonable charges? Go by tonnage or go by pieces of drawings?