1.) Look for underground guides, brochures/coupon books, and cheap budget books on the net at Amazon or Alibis. Brochures and coupon books are free. You can find them at the airports, news stands and there are on-line versions. There are coupons fro dining, shopping, and just about anything else you can think of
Underground book to Kauai http://www.explorekauai.com/
Cheap eating http://www.amazon.com/Adventures-Cheap-Eating-March-Egerton/dp/096377090X
2.) Find free attractions. Do a google search under "free things to do in Hawaii" and several sites come up.
http://www.hawaiiguide.com/freedo~1/freedo.htm
http://www.keepandshare.com/doc/view.php?u=67050
3.) Check out Hawaii Vacation Rentals on any of the islands. One site does this for you. There are a few places that gets your cost way down (and who doesn't want that). Another way to make this a fabulous trip is to get a group together and split the cost. Some of the larger estates will make you think your are kin to the Queen and the yet give you your own kitchen. http://www.pacificislandsreservations.com
4.) Buy a multi-attraction card that gets you into most of the attractions at a reduced rate, includes dining, shopping, and services.
Maui - http://www.gomauicard.com/?GCID=S18000x078-VaKHim1&KEYWORD={keyword}&MATCHTYPE={ifsearch:search}{ifcontent:content}
Oahu - http://www.gooahucard.com/packageinfo/
Entertainment card - http://www.entertainment.com
5.) Listen to and Live off others experiences. There are amazing articles are all over the internet! Here is one for 20 things to do under $20 http://www.budgettravel.com/bt-dyn/content/article/2005/06/04/AR2005060400838.html | 
