This is a long walk from the car park to the green sand beach. It is not too hilly, but there are some long inclines. There are enough 4 wheel drive vehicles that make a good trail to follow. We went on a sunny day so it meant sunny and windy long walk. Bring water. You will need it. It took us 45 minutes to the beach and 1 hour back to the car. It was worth it. If I were to do it again I would plan on staying at the beach and swimming in the cove and spending the day there with a picnic lunch. We went there as a side trip on our way to Hilo.
It was a Sunday when we went there so it may have been influenced by the weekend, but there were 2 trucks driven by locals who were willing to be the taxi to ferry people to and from the beach. Cost? $10 each. They said it was for both directions or for just the ride back. I'm sure that changes depending on the mood.
It was good exercise and I definitely got my 10,000 steps in that day.