I have never done a non-profit cook, but see if you can network with a few local butcher shops. Maybe you can work a deal to get a little from each instead of all of it from one source.
Be sure to let them know what you will do for them. Free signage at the event or on a website. Something like that.
Meat isn't cheap
2 - WSM 18.5, 1 - WSM 22.5, and 1 - ECB Smoke n Pit.