Sounds like a good price. They are quite rare, but really only interesting as a collector's piece or a curiosity.
They have an electric motor which cocks the spring instead of using the shooter's muscle power. According to legend, they are noisy, whirring Heath-Robinson devices which are not terribly reliable, powerful or accurate.
They may have been a good idea for a disabled shooter who might not be able to cock a springer, but this would only make sense in a world where CO2 guns and PCPs didn't exist.
You could buy and probably sell it on for a little profit, or buy as a 'look at this biazarre mooncalf of a rifle!' conversation piece. Sort of like an airgun Sinclair C5.
http://www.airgunbbs.com/forums/showthread.php?t=305087
http://airgunner.org/?p=145