That's if you wanted to get Wings of Liberty and Heart of the Swarm together at a discount of 42%. There's a Digital Deluxe Edition which nets bonus in-game items, including a WoW pet.
It's understood that Blizzard will be making a more official announcement about the March release date soon. The Battle.net date was spotted by Eurogamer.
Blizzard have also posted a 'Heart of the Swarm Presale FAQ' to answer questions about the Digital Deluxe edition, and other salient queries. Included in the Digital Deluxe package:
■ Three StarCraft II Swarm-themed Battle.net portraits
■ StarCraft II Zerg Ultralisk “Torrasque” skin
■ World of Warcraft Baneling Battle Pet
■ Diablo III “Blade Wings” item - Queen of Blades-styled wings for Diablo III heroes
■ Diablo III Zerg banner sigil
StarCraft 2: Heart of the Swarm adds the Zerg story campaign to the mix, with a third and possibly final addition to the sequel RTS named as 'Legacy of the Void' which follows the Protoss.