My friend wants to have Christmas lights flashing to the drum beat during his concert. What's the cheapest and most effective way of doing this without a lighting console?
You can actually build, extremely cheaply, a color organ or VU Meter with different color lights in it. The parts are readily available, often in kit form. I would refer you to qkits.com or a similar site. Outside of that you aren't going to find anything cheaper. It will require skill and patience, however.