What would be the most cost effective way for six people to travel between the airport and Airlie Beach?
Either the bus Whitsunday Transit or smaller bus whitsundays2 everywhere. Check your accommodation as some also have transfer buses.
My partner and I got a shuttle bus service which our hotel had available as an added option. A shuttle bus would probably be your best option. Alternatively you could consider a taxi - across 6 people it would be quite cheap. The drive is only about 30-40minutes.