3 dollars for 100 wings? I call shens.Me, my brother, and a girl who isn't shy about eating BBQ once put down 100 wings.
If its an appetizer, I usually eat 5, if its a meal, usually around 15-20. If drinking is involved, as EngenZero said, throw every estimate out the window and go by time. If its quick eating and drinking (less than an hour) then probably about 20 a person. If its something thats goign to be for many many hours and there's drinking involved then it could be as many as 40-50 a head for them all to be totally happy.
Obviously your budget should play a part of this. I was always fortunate to live in an area that gave great discounts for bulk and ordering ahead of time. The place would do 100 wings for 3 cents a wing. Good stuff too!