Southwest has round-trip flights from Austin (AUS) to Denver (DEN) for $98, NONSTOP. $49 each-way. Flights from November to February. Mostly midweek. Origin/Destination reversible.
Note: You can save up to an additional $125 if you book your Flight+Hotel together as a package on Southwest Vacations and use the ‘125DOM19’ coupon-code at checkout. Before you commit, always compare the prices of the individual Flights and Hotel with other hotel booking sites like Hotels.com or HotelsCombined.