a good quality theremin is not cheap!!!
if you want one just for making noise check this out...I have one on the way to put on my board
The Electro-Faustus EF102 Photo Theremin captures the magic of the original Theremin, while putting it into a modern form. The EF102 uses a light sensitive photocell to control pitch. Add a little reverb or delay, and amaze your friends with its otherworldly sounds. New features include: powered by 9V battery or regulated power supply, triangle/square wave tone option, silkscreen graphics, and input jack to allow A/B switch funtionality so you can plug right into your effects chain. http://youtu.be/ZY6yONT_S4Y http://youtu.be/ozTxKjAfMPY
I know I will when it finally gets here!!