Ask for a pecentage of "the ring"---
That is, the amount of proceeds from the Bar.
There's a big profit from selling beers and cocktails-
If a band is bringing people in, they're going to drink, and some of that money should be channeled to the Band, who should inspire people to "get happy!"
I lead a project once where in order to perform at a venue I considered a hot-spot, I cut a deal with the owner- A minimal guarantee plus a 30% ring from the hours we played-
10-1.
I needed a drummer at one point, and a few I knew balked at this pay-out, turned the job down. Their Bad.
I was right! The minor guaranteed pay-out was nicely augmented- more than TRIPLED!! for each player.
Beers sold for at least $5 or more (Imports!

); shots or cocktails could be Ten bucks or more...There were also appetizers (Sweet potato Fries!!

etc) from the bar that upped the ante.
This was a pretty high-end place, nice decor, upscale crowd, etc, and Friday nights it was jumpin', a live R&B band w/ hot Lady singer made it more so! The cash register at the bar got hot from all the action!!
Even in a small local bar, asking for a percentage could be significant.
Remember..."the ring" may be the thing!