There are a number or pros out there who will tell you that working for free is silly if you want to be taken seriously. They might even sneer at you a bit if you mention you are going to do it for some event or reason they don't care for or understand.

Last night I went out and did such a thing. I was on the bill with people who have been on international TV, won awards, and in many of their own rights are legends in history. For someone like me, who ain't shit in the magic world, to be associated with those folks and allowed to bring my special brand of craziness to a room full of receptive strangers was well worth it. Sometimes I would rather have a memory and a good time instead of a paycheck. (Luckily enough for me I have the freedom to choose these times for myself)

Sometimes a good cause is defined by you just cause' I guess.