Yes, we've done a day trip to the Big Island, but will your friend still want to go if there is no volcanic activity to see? If not, you might want to wait until you get to Maui and then decide. Although, whether or not the lava is flowing, the park itself is fascinating with tons to see.
We took a very early flight over - 7 a.m. I think, and an evening flight back, to make the most out of our visit to the Volcano Park. We found that an air/rental car pkg. was the best deal, but interisland airfare is expensive these days.
You absolutely do not need a tour -
Hawai'i Volcanoes National Park is really perfect for driving yourself and renting a car is much cheaper than the tours. When you enter the park there is a visitors center with maps, movies, displays and Info. and then there is a circle drive of the park with many interesting stops. The park is about 45 min. from the Hilo airport.
If the lava is flowing, it is REALLY hot out there, so I recommend that you 1) hike out to the lava flow first thing in the morning, the earlier the better, before it gets too hot, 2) and then drive back into the park and have a picnic lunch, 3) and then do the circle tour in the afternoon, in the comfort of your air conditioned car.
Go prepared for real hiking with appropriate clothing, footwear, hats, sunscreen, and plenty of water.
I would pick up a picnic lunch and cold drinks and an inexpensive styrofoam ice chest on your way to the park. You can also eat at the park hotel -
Volcano House, which is expensive and busy at lunch time, or for a much more casual and reasonable lunch, eat at the nearby military R&R camp -
Kilauea Military Camp, which seems to be open to the public. (We had dinner at their buffet this summer and it was full of families, children, and locals, and it seemed wide open to the public.) There are no gates, guards, or anyone asking for ID. It's not a military base, it's an inexpensive place for those serving in the military to go on vacation.
