$450 seemed reasonable to me, considering what I'll be adding it to.
Unfortunately, that price has since expired since he never PM'd me.
Not sure why it's curiously high? One reason - the seller (unwisely) states he is accepting paypal. So I question any absurd offers on that basis alone..
The other reason - even when you made your offer, there was no chance you were going to get it before the difficulty jumps to 515-520'ish million. So you make about $40 in a week, then a week after that you make $30, and so on. It uses ~300 watts of energy. It takes up space. So maybe you're wagering that bitcoins will jump in price to $1000 within the next month or two, since that seems about the only way that hunk of junk would be worth $450.
But then, in that case, you'd be better off spending your $450 on bitcoins right now.