In regards to Hayman Island, they're listed in the Australian Entertainment book, so if you have an Entertainment card you can get a discount for 5 night or longer stays, the listed rates for January 2005 (after 6th of January - before then it's rack rate only) are (in AU$):

Pool Wing Superior: $625
Pool Wing Deluxe: $695
Lagoon Wing Superior: $695
Lagoon Wing Deluxe: $745
Beach Wing Retreat Room: $695

Other room types not listed don't get discounts unfortunately.

You can also take a look at www.jetstar.com/hotels to see some good prices for Hayman Island and Lizard Island as well, at least discounted from the Rack Rate anyway. Number_6 is right about costs at Hayman Island though, you can easily spend the room rate again on food and drink costs for two people (fortunately Lizard Island is an all inclusive experience).