I've got a few calls for fill-in work over the last several months. Trouble is, if you don't know the material already and have to cram and learn everything in a week or so (or less) and only get offered $100, and have to drive a long way to play the gig, its just not worth it IMO. If I had 1000 songs in my memory bank already, OK. But I don't. OTOH, if a person were willing to work his/her tail off for next to nothing, learn 40 songs really fast, that person would be getting more calls, and maybe build on that to be able to demand better pay. Or maybe not. "He'll do it for cheap, lets call him again".