Most of the time the purchase process (docs/worksheets) pull their Cost information from the Last Direct Cost Field on the Item/SKU Card:
The Last Direct Cost field will be populated the next time you post (Invoice) a purchase document with a line for the item.
If the Item is new, try populating the Last Direct Cost field with your desired Unit Cost for the Item, which should then populate your Req. Worksheet line for the Item. You will need to delete and re-enter the Req. Worksheet line to get the line to validate with the updated data.
As Kim mentioned, if there are Purchase Prices defined for the Item, the system will fill the Direct Unit Cost on the Req. Worksheet line with the Purchase Price value.
