Additional consideration in excise valuation alters transaction value unless absent; notional interest on advances excluded absent evidence. The taxable value of excisable goods sold under section 4(1)(a) is the transaction value plus the money value of any additional consideration from the buyer; additional consideration includes apportioned value of buyer-supplied materials, tools, designs, packaging and related inputs not included in the price. Sales below manufacturing cost are deemed transaction value if no additional consideration flows. No notional interest on advances is added unless there is evidence that the advance caused a reduced price or special discount.