"Just wanted to give everyone a head's up that we are currently targeting to release Curse of Naxxramas during the month of July," wrote Aratil on the Battle.net forums. "Unfortunately, we still have a lot of implementing and bug fixing to get through, so please stay tuned!"
Curse of Naxxramas was announced back in April as a single-player adventure for Hearthstone with an expected release sometime this summer. The expansion will add new cards, tweak classes, and introduce a single-player mode consisting of five wings of a dungeon for players to work their way through. The first of these wings will be free to all players, while the others will require players to pay using either real-world money or in-game gold (which can be bought outright or earned by playing).
Pricing details weren't announced at the time, but it sounds as if we don't have much longer to wait for more information on that front. According to Aratil, "[W]e are also targeting to reveal pricing details regarding Curse of Naxxramas next week on July 1st, so please keep an eye out for that."
Following Naxxramas' announcement, Hearthstone production director Jason Chayes told GameSpot that players will, with some patience, be able to access all of its content without paying a dime if they so choose. "We basically wanted to make it that no matter how you were experiencing Naxxramas, you were able to unlock the various wings for free just by earning the gold and unlocking it," he told us in April.
"That's an important philosophy we have for Hearthstone, is that if you choose to never put in a dime, you can still access all of the content over time. So that is a core part of how Naxxramas is designed. Beyond that, though, if a player is interested in getting to that content a bit faster, they can spend a bit more money and access it as well."