This guy is spot on.
you'll have to get used to the idea of making the most out of the opportunity just to have you're music heard in a live venue. the money you receive will be made off of your merch, cds, shirts, whatever. expect to do nothing but lose money or break even for the first 20 shows. after you get a consistent folllowing of MINIMUM 40-50 people, then you MIGHT start making a bit off the door at some very small clubs. probably in the neighborhood of $20-$100, no more unless you really rock the joint, the ladies go crazy, and dudes buy a lot of drank. then you may make upwards of $100-150 a night, if you're lucky and the bar is generous (which they usually aren't).
good luck, though.