Glass Armonica

Nah, just a dremel tool, a motor or foot pedal design, mom's best crystal glasses, and an erector set. Added bonus: you can suit it to your piece/your piece to it, so it'll be idiomatic for that instrument.

But then you're the only one that could play it. Still just as possible to do (as long as you find the right size glasses) as making a homemade 5 octave xylophone. Won't be great, but it'll get the job done.