Just to let you know how it works, Jock--60 people see a show and each calls all their friends to tell them how it was, and they call their friends. And the circle is a big one---an hour drive is no big deal to go see someone that you want to see--that works out to be 120 mile radius. LesB lost more than money, too, because a low turnout and a bad show has a negative effect on the turnout for his future shows, at least the ones by "emerging" acts--
The very least you should do,Les, (other than change your contract in the way Charlie Baum suggested) is to call the booking agent that pawned these losers off on you, and tell him(or her) what happened--chances are, these clowns are doing this on every stop of their tour. They stiffed you for the sake of a few drinks and a meal, and they probably don't have a clue what they did to themselves.
I have put together many concerts and series and it takes a lot of work to fill up those seats--there is a balancing act between what the act draws and what they cost--usually the act will do what they can to make sure you do well because it means they'll be able to come back--