The cost to add an additional driver to a Hertz rental can vary based on several factors, including the rental location and the policies in place at that specific Hertz location. Typically, there may be a daily fee for each additional driver added to the rental agreement. Some promotions or memberships may waive this fee, so it is important for customers to check the specific terms when making a reservation or at the time of rental. Additionally, there are certain eligibility requirements for additional drivers, such as age and valid driver's license status. For the most accurate and updated information, it is advisable to refer to the Hertz website or the specific rental location details, as they will provide the latest pricing and policy information.