I have been Hayman Island 3 times it was nice to stay there but however it is bit expensive but worth it.
Hayman Island own Hyatt Hotel it was heaven because the hotel is infront of huge pool lookout though the beach which is very romantic. I have been swimming and sunbake (was doing tan on my body) didnt do much anything just relax away from the hassle and stress.
If you want to know where Hayman Island is ok here I tell you, Hayman Island is about 7Km (ocean) outside of airlie beach (near bowen between mackay)
How to get there, you can get public ferry or private boat or a small plane or a helicopter to get you there.
If you want visit there only one day (not sleeping there) it only cost you $30-70 because of the cost to keep the island clean and usage etc.