I get a pretty decent Cello sound by running my Theremin through a talkbox, with the tube stuck in a plastic water pitcher/jug. One pitcher works particularly well. There are so many unique sounds that can be acheived depending on what you place the tube in.
Instructions for cheap talkbox construction can be found here (http://www.youtube.com/watch?v=9EIQxwotn3k).
Instructions for cheap talkbox construction can be found here (http://www.youtube.com/watch?v=9EIQxwotn3k).