The production cost of a single layer BluRay disc will run you between two and two and a half dollars. A double layer disc probably runs closer to three dollars. Being that there is another step involved. Beyond that the licensing fees are highly debatable. I ran a search of these figures not too long ago so they should be quite solid.
The Cost of a DVD last I heard, and this was ages ago was a little more then a dollar per disc. That said however it probably hasn't gone much lower. In fact it probably went up. The deciding factor being the cost of petroleum needed for the plastic.
So to answer your question the new disc costs twice as much as the old DVD. Though as others have pointed out it isn't production costs that ratchet up the retail price. That is all the licensing involved. Which is probably going to hold stronger sway then most expect to offset the incredible losses that were absorbed in winning the format war.







