There are 7 buses per day between Sonai and Kubura, 3 of which continue on to make a full circuit of the island of the west half of the island, but there is no public transport on the eastern side. Somewhat incredibly, all buses are free.
2 taxis are also available, and a circuit of the island by car takes about an hour. There are at least 4 or 5 different rent-a-car places, including SSK (http://www.rik.ne.jp/ssk/...) right in front of the airport from ¥5000 for a full day, and motorbikes and bicycles are also readily available.
More or less all diving shops and lodgings offer free transfers to and from the airport if you book ahead.
