The Cost of a Product is entered when you create the Product as an item to be sold in your Store. This is tracked for Accounting purposes. The Cost is what the booster club paid for the item to stock it in the Online Store or Cashier Store. For example, if the booster club paid $5 to put a T-shirt in stock in the Store, and then wants to sell it to customers for $10, the Cost is $5 and the Price is $10.