It was a limited edition run, that really did not work out well. The demand for this model is much greater than was projected, and the model sold out in less than an hour. So what now? Well, one has already been spotted for sale for $500 on ebay.
So if you want it this model, now that its sold out, its going to cost you. I will be honest here, and I hope that no one buys this, and that GW comes out with another Void Shield Generator model. $500 is getting a little ridiculous.
http://www.ebay.com/itm/Games-Workshop-Void-Shield-Generator-Warhammer-40k-/151260786824?pt=Games_US&hash=item2337d87088
Already he has had 15 offers and declined 14 of them.