I would normally be looking at around $300+ HNL-LAX/SFO in September. You might get better pricing with two end-on-end tickets than as one ticket.
Deep discount ticketing to most places seems to only be available 2-3 months out right now on most carriers. For instance, HNl-PDX is $440 on HA April 18-June 8. It seems that late September should be about the same demand, but you may have to wait until late July - early August to get it for that. You could try bidding that amount on Priceline now, you might get it, or you could wait.