Denormalize Design Modification
If you move these additional costs to ShoeInventory then they will be associated with your ShoeInventory entity. This entity also has a relationship with ShoeSize. If I understand your schema (and I might not, so correct me if I'm wrong), the implication of this is that different sizes for the same shoe type could potentially have different sub-costs. This might give you extra flexibility, or it might make things more complicated. If you want to separate this data from shoes and don't want it attached to any other table (in case it doesn't make sense), you could create a shoeCost table:


shoeCost
---------
  id (PK)
  shoe_id (FK to shoe.shoeId)
  leather_cost
  manufacturing_cost
  inventory_cost
  total_cost (this could be a computed column of
              leather_cost + manufacturing_cost + inventory_cost,
              if it makes sense to do that)