We are going to Maui this year and the Big Island next year. It just occurred to me to take our US National Park Pass with us. They charge $25 for parking at Haleakala National Park and $25 for parking at the Volcanoes National Park. If you have it, take your National Park Pass for the Hawaii National Parks. And, don't forget to take it out of the rental car.
Happy Travels!
Happy Travels!