[10/08/2019 @ 2:23 PM CT] Still available. Updated example dates.
Alaska Airlines has round-trip flights from Dallas (DAL/DFW) to Portland (PDX) for $177, NONSTOP. Flights January to March. Mostly on Tuesday, Wednesday, and Saturday. Extended Weekends available. Origin/Destination reversible.
Note: Carry-on bag is allowed for free on Alaska Airlines. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.