I don't own a bow shop, but I do own other businesses and knowing what your competition sells items for, is good. Sure, go ahead and tell him. Just say you wanted to give him the chance to get the sale, but it's not worth $100 extra, to do business with him. Be honest, if it offends him, he's a poor businessman. If he simply can't do it, at least you gave him the chance.

Personally, I not only want to know what my competition is selling items for, but I want my customer's view on any differences. He may decide to lower prices, or to simply not carry that item anymore. Either way, knowledge of his customer's views gives him the ability to make a better decision.