As for now, the unit price for a purchase line for a subcontracting purchase order comes from the unit cost of the work center for the subcontractor. However, sending more pieces to the subcontractor often results in better prices. This is possible to define in sales price lists, purchase price lists, etc. but not for subcontracting.

Therefore, I suggest to implement subcontracting price lists, where the prices for subcontracting can be defined just as it is possible in the the other price lists for sales and purchase. For example, to define different prices for different items in different quantities.