Just visit nwa.com and look up trips on the weekends that you are free. Sometimes, Las Vegas, Orlando, or Fort Lauderdale are cheap. Also see where Southwest flies from Louisville and check the NW fare on that route. For example, I think WN flies SDF-STL and STL-MCI (Kansas City). So check NW SDF to MCI.

SDF has cheap fares compared to many cities like Albany and Rochester, NY and Jackson, MS or Montgomery, AL.