I did a quick look to see what it was worth and it appears ones with nice shinny paint go for between $40,000 and $50,000.
As to the value of these cars because of it's age those last years (the third generation 1973-1977) were never much in demand. Big, heavy and low HP (this one is 245 hp). Start of smog equipment. If anything happened to them they were crushed because there was no demand. Because of all that there are probably not a lot of them around and are becoming more collectable. It's so ugly it's beautiful.
As the car was his mom's car and they (his family) have owned it since new there is very small chance that he will ever sell it. He doesn't need the money.