What are you trying to spot at 400 yards? I ask because the answer changes things by about 500 dollars If you are trying to spot .17 caliber holes, then you need the top of the line Nikon ED or even Ziess. If you are trying to tell if it is a spike or a doe then a more basic Nikon may get you buy.
You buy a spotting scope for reasolution, not just magnification. How clear you can see things is often more important than how big something is. Think of it this way... You have a fifty dollar bet with a friend... The bet is that there is a typo, and somebody put a comma where a period should be... .or, for fifty bucks... Now, the rest of the problem is that the boss is holding the paper and you sure as heck are not going to bug him! Its not like you can walk up and put the thing under a magifying glass... Even if you make the thing bigger, if it is blurry it will still look like a period, and you loose the bet. It has to be bigger and clear.