I'd go with 3-3.5". No more is necessary, and arguably compromises control. For me the formula is a full-size handle with a modest blade.
Someone mentioned disposable knives - weird, and not appropriate for a gift. A quality knife made of quality steel will need the edge cleaned before it needs to be sharpened. You can do A LOT of cutting as long as you keep the gunk from drying on the edge bevel. Yeah, stick with a fixed blade for a dedicated hunting knife.
There should be a number of solid factory options in the ~$100 range. You could get an excellent custom for ~$120-$175.