The typical bar expects the entertainment to be about 20% - 30% of their costs. You do $10k in 4 hrs in bar, they should pay your band $2000 - $3000. A fancy yuppie cougar bar maybe be able to do those numbers but not a typical venue I am use to playing. They get 4x markup on bottled beer but can take a $5 bottle of shelf vodka and get $40-50 out of it. A $500 band only has to bring in an extra $750 or so to make it worth having you there.