Looks like the Swivl (http://www.swivl.com/
$199 for the swivel unit and one marker.
$19 for AC adapter.
$44 for a second marker
In the description of the use of a second marker: "IR technology used for tracking is a “line of sight” technology."
So the marker probably sends a modulated IR signal and the base has two receivers separated by a wall. If only the right receiver gets a signal, turn right . If only the left receiver gets a signal, turn left. If both get the signal, you're pointing at the marker. If neither get a signal you have gone too far out of frame.
Be sure to get the receivers that can handle continuous signals. Most basic IR receivers such as used for remote controls will ignore continuous signals to avoid interference. You could also get more precision if you use IR phototransistors and bandpass filters to get an analog signal. Then you can use the relative strength of the two signals to control speed of movement.
The motor will be something like a servo. If you use a light camera like a webcam you could probably use a hobby servo for positioning.