key tumbler??

All of a sudden, my key wouldn't work. Will turn, but won't start...there is a click. Used the plastic key and turned over...sometimes with regular key too. Took to dealer and they want to replace the tumbler for $275!! It seems to be loose, like someone messed with it. Can it be removed and replaced, or tightened up to correct position? I want to try anything before I hand over that much money!