1. Edit the item
2. Click "Costs"
3. Click "+ Supplier"
4. Either "Add As Main"
5. Or click "Add" for a non-main supplier
6. Click "×"
7. Edit the lines to put in a different cost per supplier
8. Click this field.
9. Or leave empty
Adding a Supplier or Supplier(s) to an Item
Set one or more suppliers for an item, an optionally their costs