theres a load of chinese cheapo fake samsung covers on ebay.co.uk with the window. Its not clear whether these are smart windows like OE or whether the NFC works - i suspect not. You gets what you pays for....
Although I've paid through the nose for the Samsung OE case on the note 2 and they are frankly crap. The edges come apart with 2 weeks! I've tried 3 now, all replaced under warranty. Sammy OE is not necessarily better.