Southwest has round-trip flights from Houston (HOU) to Denver or Atlanta (DEN/ATL) for $98 or $110, NONSTOP. $49-$55 each-way. Flights from August to December. Most flights are midweek. Atlanta has Saturdays available. Origin/Destination reversible.
Note: United, Spirit, and Frontier may have fee encumbered “Basic Economy” fares available for a bit less. Keep in mind that those “cheaper” fares are often more expensive once you factor in bag fees.
Note: Southwest doesn’t charge a change-fee, so if you already booked this flight, but paid more, you should be able to re-book at the lower price and get the difference paid back to you in the form of a travel-voucher.