One tip is to consider nesting flights. If you plan well in advance, this may be less of an issue, but on shorter notice, something like Monday night out, Wednesday night return itineraries can be costly. You could, for example, buy the following:

Flight 1:
PDX-SFO Monday week 1
SFO-PDX Wednesday week 2

Flight 2:
SFO-PDX Wednesday week 1
PDX-SFO Monday week 2

That way, both trips include a weekend stay. Not sure if this makes as big of a fare difference as it did 20 years ago, but worth researching. You'd generally have to do Flight 1 and Flight 2 on two different airlines if you'd run afoul of Saturday-night stay restrictions, but if this is a long-term plan, you could build up status on two airlines, if there are two carriers that make the trip round-trip, e.g., United and Alaska, which are good complementary programs. There are advantages and disadvantages of this strategy.