It entirely depends on when you are traveling (high/low season), if you got a good deal, how far you booked it in advance, if your ticket was round-trip or one-way, and what airline you chose.
Most airlines offer deals during different travel times, especially if it is not peak season. If you wanted to go to Oahu in January, the flights would generally be between $300 and $500. Try checking travel sites that offer "low-fare" calendars.
alaskaairlines.com (yes, they fly to Hawaii)