From microsoft's website:
http://windows.microsoft.com/en-US/windows/shop
That's the price for Windows 7 Ultimate, and that's what you need to pay if you're upgrading from Vista. Sure, you can update from XP as well, but the only option if you want to upgrade from vista is this.
I'm comparing with Ultimate, because that's the full product without cutting any features out. OS X only has a "ultimate" version since it always comes full featured.
edit: And even if you compare to the cheapest option, it's still more expensive at: $119.99
As I said in the previous post, the latest 3 versions of OS X combined cost $78.98 and you can install them in as many macs as you have. As opposed to only 1 PC for windows 7 ultimate, and there are no "Family Packs" for this "flavor" of windows.