A company called
Marlin P. Jones & Associates deals mostly in surplus and discontinued electronics. In their latest catalog, I noticed a wireless security camera (their stock number 15052-ST) and receiver for $79.95. Just add a TV. A big advantage is that you don't have to string coax from the stage to the booth. The range is supposed to be 250 feet, and it operates in the 2.4 GHz band, well away from anything used by wireless mics. They also have wired cameras pretty cheap if you're inclined to go that route. I bought 8 board-level cameras a video switcher and a time-lapse VCR from them for my home-security system, and was pretty happy with what I got.
John