My key just one day stopped turning in my ignition. Any idea why?

all of the obvious things have been checked like my wheel being locked and I'm securely in park, I've tried lubricant on my wheel. When I stick my key in the ignition (of my 2002 focus), it beeps when I have the door opened. So it recognizes a key is in there, but won't turn. Do you think this is a key issue or an ignition issue? To get my key replaced I have to get my car towed to the ford dealer and it's gunna cost me 80-90 to get one made. Will they be able to tell me Wether or not it's my ignition vs key at the dealership?

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