Frontier has round-trip flights from Dallas (DFW) to Denver (DEN) for $33-$47, NONSTOP. $18 each-way. Flights October to November. Departures on Tuesday, Wednesday, and Saturday. Extended weekends available. Origin/Destination reversible.
Note: Frontier fares do not include a free carry-on bag. Only a small personal item, like a Jansport City Scout backpack is free. You can avoid paying for seat selection if you accept the randomly assigned seat prior to boarding.
Note: Frontier seats only have 28-inches of pitch; 2-to-3 inches less space than most other airlines.