Item costs and subcontracting

Each of above items has a BOM defined to include printing cost. After a 
PO is created, we have to transfer material to supplier and in PO when I
 select "Transfer > Material to Supplier" it asks for the item where 
we want stock to be transferred and this has to be done for each item in
 the PO. Lets say a PO has 20 items. I have to transfer material to 
supplier 20 times to complete the subcontracting. 

You can transfer 20 qty or even 20 items in a single transfer entry. Can you please elaborate issue faced at this steps? Screenshots will be helpful as well.

All I want is to include any associated costs in items so when final 
item arrives in the warehouse, its valuation rate reflect costs 
associated with it. 

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