Microphone to amplifier to FM transmitter to boombox speaker. Oddly if I move the mic any further away the pitch seems to change randomly based on distance, I think it might have to do with the acoustics of the room or something.

I just pulled my friend for Secret Santa, I was thinking maybe a really weird and Large instrument. We are trying to spend less than $30 is the only problem. I saw theres something called a didgeridoo, but i was wondering if there was something else? Not trying to offend anyone here, but maybe a super useless instrument?