Building Theremin

A Theremin is a music instrument that is used by bending radio waves, I am building one for my high school band, Palm Bay High School Marching Band, to experiment with  but the parts add up to about $500, I do not have the personal funds for it so I am asking you to help me! Please and Thank You. We are a small band of about 60, and we are wanting to experiment with a Theremin because it would be a new experience. Also here is a link to a video of a Theremin being played on Ted.