The rate of the motor vehicle excise tax is four percent and is applied to the price paid for the vehicle. If the price paid does not represent the value of the vehicle in the condition that existed at the time it was acquired, the tax rate shall be applied to the reasonable value of the vehicle in such condition at such time. However, allowances granted for vehicle trade-ins may be deducted from the price paid or the reasonable value of the vehicle purchased.
NMS § 7-14-4