How much work do you expect your chaperones to put in?
Is this just a quick out and back trip for a performance, or a multi-day tourist trip that includes a performance?
When we did 4 days in NYC a few years ago, chaperones paid less than students but enough to cover their hotel, meals, etc. I had more parents offer to chaperone than I needed. Last year we went to San Antonio for an overnight and a performance, and I couldn't get enough parents to make my district-mandated ratio. The boosters had to cover a large portion of the chaperone cost.