Alaska Airlines has round-trip flights from Dallas (DFW/DAL) to Seattle or Portland, Oregon (SEA/PDX) for $197, NONSTOP. Seattle flights from September to November. Portland flights in August. Departures on Tuesday, Wednesday, and Saturday. Extended weekends available. Origin/Destination reversible.
Carry-on bag is allowed for free. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.