Back when there was competition between airlines for interisland flights, we used to see airfare wars like this one between Go! and Hawaiian:
Between today and September 30th, 2009, travelers can fly interisland on Hawaiian for $25 each way. The price of a one-way fare hasn’t been thus low since Go! entered and undercut the market in 2006.
The catch is that you have to be a member of their loyalty program.
Today a similar airfare sells for over $200. Hmph. I miss those days.