You can have a great time on Airlie Beach really cheap and even free, there's lots to do and here's what you can choose from.
Tour on a speed boat of the Whitsundays
Go to the lagoon
Go some snorkeling
Do a little fishing
Have a swim in the sea or sunbathe (FREE)
Go on a jet ski tour
Go on a Heli ride (costs a little but well worth it)
There's lots more to choose from. You can see more Airlie Beach things to do cheap or free if you follow the link.