I forget if the premium was dollar based or Bitcoin based, but I paid a .92 BTC premium when I purchased mine direct when they were sold from Alitin.
From my recollection the price was bitcoin based, it never changed from the 0.92 BTC premium throughout its official listing.
Using web.archive.org, I can see snapshots of the listing between December 2013 and November 2015. I am not sure exactly when they started/stopped taking orders but the value of bitcoin in that time included the end of the 2013 all time high being
~$1000, the lowest value being
~$200