IDTRAVLER a good birch bark horn will work wonders when calling Moose. You can roll your own and either tie or staple it into a cone. My dad has made horns for many years. You will find that the longer, narrow horns will reach further with the sound, but the shorter wider horns will be easier to carry with you.
As for making the sounds of a Moose, it is not that difficult to make them with your own voice. This is a sample of what work you can do into a horn, but you do not have to go this great a detail. To me a horn, espically after you have called in a moose or two will become the focal point of your stories. This is why I like my dad' s horns, last last for many years.

Good luck in what ever you deceide to do, weither it is mechanical call (if it is legal), hand made call and your voice.