I just got one on eBay today for $20. Real thing? I don't know, doesn't really matter to me that much. But I'd rather buy a $20 repro than pay $120+ for the genuine thing, that works exactly the same. As I've said, I'm not really a "collector", I'm a "gatherer".
I mean, look at some of the prices here, especially for those flip sights. That's just nuts! http://www.m1carbineparts.com/
But, that's JMHO.