One of the problems is the 12:15 outbound doesn't have any low fares available. The lowest available fare on the 12:15 nonstop is a B fare, which is almost full fare. The other non-stops have Q fares available. The 4PM non-stop has V fares available. Try the other outbound flights. It's surprising that the 12:15 outbound isn't offering any discounted fares on that day. The morning non-stop is usually the most popular outbound flight.
I don't know what your return date is, but if it's 12/23, I found a fare for under $800, returning on the redeye via LAX.
There are no S or T fares. Those are the cheap ones.
You have a Mileage Plus number, right? If you want to see the available fare classes on united.com, go to
www.united.com, logout if you're already logged in, then login on the right side of the page, selecting "shop for flights" in the pull-down box. You have to use "muti-segment" itinerary and diplay availability by "schedule". You also have to set your preference to "an expert" under profile/all preferences. (scroll down to "Display Preferences"/"Availability Format").
I usually check fares via SFO-LAX-OGG and SFO-HNL-OGG if I can't find anything decent on the nonstops. I'm sure you know that already.
You might want to hold out for S or T fares. Of course there's a risk if you wait. On the other hand, I hate the red-eye.
-David