When mine did that I ordered a new key-lock from Wilkinson for $60 or so (IIRC). Replacing it isn't that difficult but requires dropping the steering column, disconnecting a few wires and drilling a hole to push out the pin that locks the cylinder into the bracket. It's a two or three (if you're a bit slow like me) hour job but worthwhile.
When my original lock packed up I was visiting a friend's house. Since I was only expecting to be there a few minutes, I rolled into his driveway diagonally, blocking the whole thing. Then my lock totally jammed for the last time and I was completely unable to even unlock the steering. The only good thing was that my friend is also a Pantera owner and I was there checking his major re-build progress. He kindly offered to just swap his entire column into my car so I could get home. That swap was fast and easy and 20 minutes later I was on my way home. Having my column completely out of the car made installing the new lock easier.