3. Product Costing Cost
Duties to be paid are based on the HTS code, the Country of Origin and the value of the goods. 
Value = Purchase Cost + Assists
Valuation of goods is another complex legal topic. In the simplest form the value of goods is based on what was paid for them prior to export but the exception are many. 
Value may be affected by material support supplied to the exporter (manufacturer, export broker, etc.) like equipment, tooling, raw stocks, commissions, future payments based on quota and more. These are referred to as assists.
The government may also have interest in the relationship of the exporter to the importer i.e. discounts among friends and family don't count! Reasonable fair market value must prevail in these situations.