Did you try fixing/ fix the order id/ purchase orders? Can you attach a sample file for reference?
That would be problematic, the default cost relates to item level information. The purchase order id covers multiple items on that purchase order (multiple lines on the purchase order).
The Default cost has to be multiplied the qty of the style by the default cost of that item , then there would be several purchase orders
You can Sum up the Quantity Ordered across all product and then multiply by Cost