Given the rising cost of EVERYTHING, I generally try to save new or slightly used grips if I think it's something that somebody can use.
Last summer I was playing in our golf league and a worker from the pro shop brought out a driver that he had re-gripped for someone I was playing with. The guy I was playing with asked him how much he owed and it was something like $25.
I told him, don't ever do that again. I've got tons of grips that I'll never use and I'll put it on for free. I'd charge someone a small fee if it was for several clubs, but for one club?... Buy me a beer next time you see me.