Greyhound USA operates a bus from Nashville to Louisville every 4 hours. Tickets cost $22 - $55 and the journey takes 3 h. Megabus also services this route twice daily. Alternatively, Southwest Airlines, Delta and 2 other airlines fly from Nashville to Louisville hourly.
From Nashville, TN bus to Louisville, KY. 3 h $24. From Nashville drive to Louisville. 2 h 53 min $21. From Nashville, TN bus to Nashville airport, fly to Louisville airport, then line 02 bus to Louisville. 6 h $459.