If you are a friend, and it is for a worthy cause, and I have the time and energy, I am open to possibly performing in a benefit. Otherwise, I will not play for free, let alone pay to play.
I can play music at home. I don't need to perform in front of others to validate my existence. My existence is already valid.
If there is interest and demand, it makes sense there will be some money offered. If not, I am fine.