Purpose: Be able to be programmed to do a demo that could entice students from school age and upwards to come to University and study engineering (electronics, instrumentation and mechanical being the obvious disciplines)

Budget: 500GBP
Must have : Must be portable desktop size as will be carried to and from exhibitions.
Some form of positional feedback.
Nice to haves : RaspberryPi/Java interface (simply because that's what I know). I'd be doing the programming.

Starter for 10 Something like this
Robotarm although it wouldn't have to be an arm.

Any bright ideas? Left field eye catching ideas welcome.