Welcome to FlyerTalk,
modeljayc! ^
I just scanned your dates into
www.kayak.com and found a $357 fare on ATA, which is not bad for West Coast to HNL.
As far as I know, United is the only major airline with a documented policy of offering a voucher for fare differentials; I could be wrong on this.
Since your question is about travel to Hawai`i on all airlines (and not just Hawaiian or Aloha, the Hawai`i-based airlines that fly to LAX), I'm going to move this over to the Hawai`i (Travel) Forum, where other FTers can offer advice.
Aloha,
FlyinHawaiian, Co-Moderator
Hawaii-based Airlines Forum