Welcome and sorry for your troubles, you should be able to replace the ignition lock cylinder with little hassle, ac delco has them, 1997-1999 Pontiac Grand Prix Ignition Lock and Cylinder Switch - Body Electrical - AC Delco 97-99 Grand Prix Ignition Lock and Cylinder Switch - 4734-05006977 - PartsGeek
You may be able to find one cheaper on ebay, I don't know. You should be able to find a simple write up on google if you need help with the anything as well.
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