Quite a bit less. An average passenger car has between 1 and 2 grams of Pt.
If you are correct, then the amount each vehicle could save would be more like $100, if the replacement mineral product were free. I might be thinking of Pd, in those converters that use it. Somewhere, I read that nearly an ounce was in one; then again, maybe that was for the huge truck converters. (Which easily have engines 20 times more powerful than small passenger cars do.)