Yes, that is still considered a slow travel time. Honestly, I'd wait for a few months before booking if you are looking for the best deal on a coach fare. Maui is a very popular destination, but I've seen one way fares lower than $200. The day of the week you are traveling makes a huge difference too... If you can travel say wed-wed then your chances for a deal are much higher.
Alaska has nonstops to Maui from SEA, PDX, SFO, SMF, SJC, OAK, ANC, as well as San Diego. The least expensive tend to be out of SEA, PDX, or SJC, and even BLI (which I didn't list as not many flights go in/out from other carriers). You may want to consider looking at all options, and SW has service to all these locations as well. One thing to consider... Alaska and SW are not partners, and chances of them checking your bags all the way through are very slim when travel is not booked on the same ticket. If you are carry on only, well, nothing to worry about.