Another very inexpensive option is a fluorescent lamp starter. Most any hardware store will have these. They come in different values, depending on the tube that they were designed for. Grab 2 or 3 different values and go home and try them.
Almost any basic light fixture will work. You simply need to cut the cord open and using the black or brown wire (or, "hot" wire if it's just 2 conductor lampcord like that found on clamp-lights). Wire the starter in line of the hot conductor and ta-da. Flickering lamp at random.
Operations Manager & Technical Director