Delta, Virgin Atlantic, and Air France have round-trip flights from Dallas (DFW/DAL) to Madrid (MAD) for $586-$599 with a connection. Flights August, September, October, November, January, February, April, and May. Departures on Monday, Tuesday, Wednesday, and Sunday. 7-day minimum stay required. Dates over Thanksgiving are available.
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.