Is the cost for each company different after the first period?
Indeed, the costs of each company will be different after the first period, but not in terms of raw materials, labor, and logistics per unit of finished goods.
Each company made investment on R&D expenses, marketing expenses, maintenance expenses, and equipment investment, and changed the market potential for its product as well as the cost (e.g. Conversion coefficient) of making the product. These are fixed costs.