I think $100 would be pretty good. It's really what you'd take. If you'd do it for supper and tips, then that's cool, too. The strategy is to start higher than you'd expect to establish your perceived value and anticipate the counter offer.
Start high. Like $250. He's a businessman and he wants to get a good deal on whatever. If he gets you for the cost of supper, then he is getting a $250 guitarist for that price.
When the guy scoffs, alot of times people feel embarassed, but you have to be prepared for the counter offer. "Look, I have reason why I want to get in places like this and I am willing to cut you a deal while we try it out. How about we do scale the first time ($35/hour) and then we can renegotiate based on how it works out for us." I always say scale like it's some kind of standard rate. I have no idea what it is, but I make it what I'd take for the gig divided by the hours.
That is assuming that you are bringing value to the table. Nobody is going to be excited about adding an expense unless it is going to translate into people staying around and drinking more, etc.