How to maintain separate price For packing material

Dear sd experts

i have one business scenario , i want to maintain separate pricing charges for packing Material

ex sales order created 25 items and in delivery we maintain packing so 25 items price in sales order 500 rs

and now once we added Packing material in delivery that packing price automatically will added into Billing 500+25 rs :525

why because some times with out packing also we can delivery the stock to the customers ( they will arrange their own)