1. GO airlines in very cheap. You can book flights with go airlines at http://www.iflygo.com/
2. normally flights on GO airlines cost 39 dollars each way; However, if you keep checking the website and wait until closer to your departure date, the prices sometime go as low as 19 dollars each way.
3. Hawaiian and Aloha Airlines are also great airlines and sometimes also have low fares, since they try to compete with GO. If it is equally cheap to book on Aloha or Hawaiian, I would recomment these airlines over GO airlines, because the service is slightly better