Seems outrageous to me, but I don't know a gnats worth about H&Rs, so couldnt say either way.
There are likely many thousands of special collector niches for guns (and other collectibles). The opportunities are in knowing something the other guy doesn't, and picking up a bargain that way.
I recently bought a rifle. I won't go into the particulars because this is the revolver forum, afterall. I found it in a gunshop and was able to buy it for about $50 more than what the commonly found version goes for. Some would say I 'paid too much', but the rifle is a version which collectors very typically pay twice as much as I did. I'm really much more of a shooter than a collector, but I sure don't mind picking up something that I can later sell for a lot more than what I paid.
Maybe the guy who paid $900 for the H&R got carried away, or is a fool, or has money to burn and doesnt care . . but then again, maybe he's a very saavy collector that jumped on an opportunity. I, personally, don't know enough to say and aren't interested enough in H&R revolvers to find out. (Theyre not my particular niche.)