You didn't give any info about the rifle so I don't know what to tell you about your friends M1. There are many variables. Age, matching parts, condition, etc.
I just paid $500 for one from a friend. He's not a collector and had just found it when cleaning out his parent's house after his mother's death. His father had gotten it about 20 years ago and was still in the original packaging from the CMP. It was a post WWII/pre-Korean War model with mostly Springfield parts. Excellent stock, but with non-matching handguards. The bore was very good. Bluing was about 75%. Mechanically it looked to be in excellent shape. And as usual for Garands, functioned like a charm. I thought $500 was a fair price given the condition of the rifle, and the fact that I could get one from the CMP for the same amount. Happily for me, he agreed.