Key turns freely / 2002 avalon

I have a 2002 Avalon and when I tried to start it the key turned freely in both directions and the only thing that happened was the dash lights came on and stayed on. I had to disconnect the battery to get them to turn off. I am not sure if I need to replace the ignition switch or the lock cylinder or both? How difficult a job is it to repair? Thanks for any information.:confused: