The Hilo International Airport is located at the northeastern corner of Hilo, less than three miles from downtown. Almost all flights arriving here are interisland, mostly from Honolulu. Rental car booths and taxis are located right outside the baggage-claim area.
The drive from Hilo to Kailua-Kona (via Waimea) along Hwy 19 is 95 miles and takes about 2½ hours. Driving along Saddle Road can cut travel time by about 15 minutes.
All Hele-On Bus services originate at the Moʻoheau Bus Terminal in downtown Hilo. From there, buses go around the island, but service is infrequent, sometimes only very early in the morning (for work commuters) or only a few times daily. If you're going to a major destination (such as Kailua-Kona or a South Kohala resort) and are staying within the area, the bus is a feasible option. Check the website for current routes and schedules.