Delta has round-trip flights from Dallas (DAL/DFW) to Sao Paulo or Rio de Janeiro (GRU, RIO) for $558 with a connection. Flights between September and April. No Weekends. Departures on Monday, Tuesday, Wednesday, and Thursday. 7-day minimum stay required.
Rio de Janeiro is missing December fares.
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.