Phord ? (sorry)

My wife has a 65 Mustang she's wanting to sell. The parking pawl stopped working.It clickes when you put it in park and will roll when parked on a slope. What would be the fix and what would be a high estimate for a shop to repair? Other than this problem it works fine. Need to get rid of this car to finance her Dart project. Thanks for any help in advance.
Bob