It’s not especially versatile or attractive – but this cardboard synth will at least make some interesting noises:

A little and cheap amplifier i built using chewing gum paper as touchpads. The LEDs are synched with the beat. the harder you press on the touchpads, the less resistance your fingers have. this way you can control the beat (left side) or make queer noises (right side).

via Konservendose, who probably saved enough money using chewing gum paper for touchpads to be able to afford one of those 10 cool electronic music instruments under $100.