Before we could make any suggestions, we would need to know what kind of hunting he is doing, what he hunts, and maybe where he hunts. There are lots of useful things a hunter could get that would cost $100 or less.
More info is needed. For example, my husband and I hunt deer, rabbits and woodchucks. We hunt in Michigan and prefer to hunt deer when snow is on the ground. We use a bow, or muzzleloader.
But for gifts for each other, it is usually not hunting related. For our last anniversary he got me a nice kimono, hand embroidered. I got him a pair of moccasins that he can wear outdoors. (We don't wear shoes in the house.)