I can almost hear accountants in the forum falling out of their seat. What a simple question...
Anyway, you are asking one of the most complicated questions in accountancy. Let's take only the manufacturer, they maintain an army of cost accountants just to answer that question.
Many smaller product companies don't even bother finding the answer to that question, if they can pay their bills they will be happy. Finding the exact cost of an item being manufactured is very difficult, it depends on too many parameters like volume, inflation, interest rates, R&D, wages, etc, etc, etc....