Hilo International Airport: Rent a car at ITO: it is the genuinely good transfer for the Volcano/Kīlauea summit area, roughly 45–60 minutes to Volcano Village or the park entrance, with typical rental-car pricing roughly US$60–120+ per day before fuel and insurance. The budget alternative is a short taxi/rideshare into Hilo followed by the limited Hele-On Route 11 (Red Line) toward Volcanoes National Park; rides have been advertised around US$2, but the timetable is too thin to treat as reliable sightseeing transport.
Ellison Onizuka Kona International Airport at Keāhole: Use a rental car and expect about 2½–3 hours to Volcano Village, longer in rain or after dark. Kona is fine if it fits a wider west-coast itinerary, but it is not the efficient airport for a Kīlauea-first trip; there is no practical public-transport transfer to the summit district.