The Kona area has major vehicle rental car companies represented and most are located adjacent to the Kona Airport. The rental agencies offer free shuttle bus service from a stand near the airport terminals. Actual drive time from shuttle bus departure to arrival is less than 5 minutes. However is it suggested that you allow appropriate time.
Some resorts may have associations with specific rental companies.
Many people enjoy the use of convertible vehicles while on vacation. Please keep in mind that you may receive lots of extra sunshine which you are not accustomed to. Also, the Big Island has many micro-climates and you may drive between bright sun and pouring down rain in close proximity to each other.
There are certain roads and areas on te island which require 4-wheel drive. Some rental companies may not allow their vehicles to be driven in those areas. Check with your rental company for details.
Also, it is bets to fill up your vehicle before returning it. There area a few gasoline stations between Kailua-Kona and the airport. If you are a Costco member, that station is also near the airport. If coming from the north resorts, you will need to drive past the airport to find gas. It never hurts to get and keep a receipt for gas anytime you rent a car anywhere so that there is no question you topped off the tank before returning it.