The same iMac costs $979.00 in the Apple refurb store. I'd say that the price is ok for a used one. Maybe you could even can haggle down a bit. Make sure to purchase Apple Care warranty for it if you want to buy - but then you'd have to be rather quick with your decision as you only have until Sunday to do it
You could do maybe a *bit* better, but I don't see how much more. I would say that is a good deal, especially if you planned on buying AppleCare (so you would not have to have any worry about buying it used).