You get what you pay for, so my standard fee is "free" and if I make some money at it, then so be it. When money clouds the issue if I should perform or not, then the fun of it all seems to vanish. Maybe thats why I am happy doing folk festivals. I think I might reach out this summer and try busking to test the waters. I do know from experience that performers who lack a CD to sell at their gigs are not takin serious as pros.
Bottom line (IMHO) is you take any and all the money that the market will bare, providing money is what motivates your music presentations.
Mudjack