I was thinking more along the lines of a cheap five-LED flashlight or several from the Dollar store for a directional beam, add some cheap 2N2222A transistors (about 10/ dollar) and an electret mic for quick and dirty Amplitude Modulation, and if you want to get a bit more fancy, add different coloured filters to the white LEDs to define different bands for separate data streams. Sounds rather fun, now that I think about it.
Here’s another thought...UV LED’s are readily available. You can boost your bandwidth just by going to 250nm.