A Whispers of the Old Gods pack

As of now, there has been no such announcement. As far as my memory reaches, the pack price has also not changed.

What has changed, though, is the Arena price. Originally (early closed beta), the Arena was called "The Forge" and required actual packs as an entrance fee instead of gold. In exchange, you would keep all the cards you drafted. And the rewards were also different. But since this was an early beta experiment, it's probably safe to assume they like it better the way it is now and won't change it again (especially since beta is over).

If we look at other big freemium games, we can see that there are frequently sales or special offers, but they usually affect real money prices only. So even if there will be such a sale or offer one day, it probably won't change the gold price, but instead alter the gold-to-money ratio.

Official word can be found here, and two posts below that:

Golden Gelbin Mekkatorque is acquired by making a purchase with the Hearthstone in-game store. It is currently still available in Open Beta. It is not craftable.

Regular Gelbin Mekkatorque can be crafted using Arcane Dust.

Golden Elite Tauren Chieftain was a part of our BlizzCon In-Game Goodies card, which was acquired by attending BlizzCon 2013 or by purchasing the BlizzCon Virtual Ticket. It is not craftable.

Regular Elite Tauren Chieftain can be crafted using Arcane Dust.

That post dates from 1/21/2014, but as far as I'm aware, there have been no changes since (except for the beta ending, so Golden Mekkatorque is no longer available).

Additionally, neither one can be drafted in the arena, according to a dev on twitter.

_{Thanks to this and this for links}