Flying in to Hilo International Airport is your best option if you plan on visiting the National Park. The flight takes around 50 minutes from Honolulu International Airport and will cost less than $100 one way flying with Hawaiian Airlines.
Once you arrive at the airport it will be necessary to hire a car (unless you know a local who is willing to drive you around). Whilst there is a bus service to the National Park Visitor Centre, that is as far as it goes and you will find it very difficult to explore the National Park without further transportation. You can compare prices on car rentals at Hilo Airport Car Rental. We also hired a GPS unit with our car, but in all honesty you will be fine using the free map that you are given on your flight and then following the marked signs down highway 11 to the National Park.
From the visitor centre, head west to the Jaggar Museum. From this museum (free entry) you get a terrific view of the Kilauea Crater. Smoke and ash billow into the air, filling the skyline. Stop to take a photo or seven and have a chat to the museum guides who will tell you all about the volcanoes and the formation of the islands of Hawaii.
Trust us when we say the trip will be well worth it! If you've never seen a volcano before this is a great 'first volcano'. If you've seen other, more explosive volcanoes, this will give you the chance to relax a little more whilst learning heaps about the formation of volcanoes :) :) :)