American Airlines has round-trip flights from Austin (AUS) to Medellin (MDE) for $352 with a connection. Flights in May, August, September, October, November, January, and February. Extended weekends available. Origin/Destination reversible.
[01/25/2017 @ 9:37 AM] Fare gone. Removing from deal list.
Aeromexico has round-trip flights from Austin (AUS) or San Antonio (SAT) to Medellin (MDE) or Bogota (BOG) starting at $312. Flights February to May. Weekends available.
Note: Austin has better routing for flights to Medellin and San Antonio has better routing for flights to Bogota. Check both airports. The example dates below will use the airport that has the best chance of avoiding a long connection time.