ORIGINAL: Champlain Islander
Easiest and cheapest way to get a good sounding call is to take an old coffee can and drill a small hole right in the center of the bottom. Put a piece of string about 2' longor old shoe lace through it and tie a large knot in the end so it can't be pulled through the hole. Wet the string and hold the can with one hand and slowly pull the string sliding your fingers down it.
Actually I think it's easier and a lot cheaper to just use your own voice. There's no need for anything but your hand cupped over your mouth. If you need to know what moose sound like I'd recommend the videos "Love, Thunder and Bull 1 & 2" by Wayne Kubat.