The Therevox is an elegant instrument made in Ontario Canada. I think it’s a sort of mix between a Theremin and slide guitar. Some have MIDI control. Depending on the model these run from about $1500 – $2000.
“Inspired by the Ondes Martenot (1928) and the Electro-Theremin (1950), the ET-4 is controlled by moving a finger along a reference keyboard shaped to provide tactile feedback. Dual pressure sensitive intensity keys control the amplitude of the ET-4′s two independent analog oscillators. Combined with a low-pass filter, white noise generator and internal spring reverb the ET-4 is an expressive and versatile performance instrument.” – therevox.com
For more info: therevox.com