Sorry to hear that, seems pretty bad conduct on the part of the band, especially the drumtard.
Us bass players are sensible and responsible folk, so I would suggest you offer to do the gig and give it your utmost, HOWEVER since it is now just business they need to give you half of the fee (or whatever makes you smile).
That way you remain professional and your reputation even increases, but you screw them on the money. If they refuse to play ball, all they could complain about is that they could not afford you.
My 2 p.