Hilo/volcano trip
I did this exact same itinerary last year. We few in to Hilo and drove to Volcano National Park. We stayed at one of the rental homes offered through Country Goose Bed and Breakfast. It was the Pukeawe Cottage and in my opinion at $150 per night was the best deal on the island.
The cottage was absolutely beautiful and clean. It was stocked with eveything you need and even had a washer and dryer. We loved it!
We drove to Kona and stayed at Waikoloa Village then arranged to drop the car in Kona so we didn't have to drive back to Hilo. It was a great trip! Have a wonderful time.