User blog comment:Madman97/ESO Update includes Shadow of the Hist DLC/@comment-24635935-20160624120357/@comment-4984687-20160627063131

On June 24's (Friday's) episode of ESO Live they said it would be released on the PTS next week, so anywhere from the 27th of June to July 1st. Official release will be in August.

It will likely be paid. I think the price is 1,000 crowns, but I can't be completely certain.