The simplest setup would be a video camera in the room feeding RF to the TV via a long cable.
That cable can be coaxial antenna cable from Radio Shack, cheap and rugged, about $20-$50. Connect the cable tot he antenna input of the TV. You set the TV to old analog channel 3 or 4. At the camera end, connect the video ouput of the camera to an RF modulator, (another $20 at Radio Shack). This turns the video coming out of the camera into a broadcast type Radio Frequency (RF) signal. With that setup, your TV will now show video and play audio from whatever the camera sees.