In order to make a Finish Goods. First i have to order Raw Materials to make it. So i create a Purchase order for Raw Materials in QBO. Then i pay the bill which increase the QTY of particular Items(Raw material). Now i have enough Raw Materials available to make Finish Goods. I send this Raw items to Finish product making company. So i create another Purchase order for Finish Goods. In this Purchase order for each Finish product the unit cost i enter is the Total cost of making it. (Raw Material + Assembly cost). The reason for this is while selling this product, the entry in COGS account should go as total cost (Raw + Assembly). 

Now i will be paying the vendor only the assembly cost and not the raw materials cost. How can i put this in my finish Purchase Order so that the total cost of PO will be only the assembly cost and not RAW + Assembly.