Delta and American Airlines have round-trip flights from Dallas (DFW) to Boston (BOS) for $179, NONSTOP. Flights in May, August, and September. Departures on Tuesday, Wednesday, and Saturday. Extended weekends available. Origin/Destination reversible.
A Carry-on bag and also a personal item is allowed for free on Delta. You can avoid paying for seat selection by accepting the randomly assigned seat at the gate.