I was able to get a quote from a dealer in Canada, the price quoted was $499.99 USD without shipping charges yet. Now this is a nice looking box, but I don't think I'm quite willing to spend $500 + shipping to get it.
I was able to mount a spare box that I had for my Kawasaki Prairie 650 to the rear of my 850 XC. It hangs over the back a little bit and I'll probably have to take the box off to service the air filter (to be able to get the seats off). Looking at the photo, I think this box would probably have to come off to get the seats off as well.
If anyone might be interested, the dealer I contacted is Broadview Power Sports Ltd. in New Brunswick. Broadviewpowersports.com
I got an update for the shipping costs. I was quoted $373.03 for shipping. Hopefully this becomes available in the US soon, $900 is a bit much for a cargo box. Thanks to the folks at Broadview Power Sports for at least giving me a quote.