It's been my opinion that anything over 200 was absurd. It's one thing to want one and pay 200 for it. There are a fair amount of people that are in that game. But I have to wonder who is buying at 400 plus.
I would think that you would have to be a serious collector to pay that kind of price. Or have some other obsessive/compulsive need to own one, what ever the price.
At 400 dollars you are way past the Realforce/HHKB crowd which is pretty insane by itself.
I still think the mini is an awesome keyboard though, but I can get a unicomp for less than 100 dollars... I suppose it's more than key feel at play here.