I agree, its a pretty common siren and they're usually worth about $50. I owned one of these units and i still think it was my favorite. For those who want to hear the siren tones, you can see the video of my siren on youtube.
They do sound good, and had good back lighting. I used one for a while before trading it for who knows what. Definitely not rare though. Any siren with a phaser tone isn't that old.