I have a function generator; it's a Hewlett-Packard but I don't recall the model number off hand. It can generate square/pulse, tri/sawtooth, and sine outputs from sub-audio frequencies up into the low megahertz. The real fun comes with the modulation inputs -- you can make it do AM, sync, and various forms of frequency sweeps under control of a built-in LFO or an external voltage. (There's an FM input too, but it can only modulate about plus/minus 10%, so not much fun for audio purposes.)
I see function generators on eBay for $300-500 US, depending on model and condition.
Switches, knobs, buttons, LEDs, LCD screens, monitors, keys, mice, jacks, sockets. Now two joysticks!