The alliance chopper will be implemented ingame, however it will cost you gold to get it! How much is currently unknown.
Due to popular demand (and a few shady back-alley deals in Stormwind’s Old Town), the Alliance bike built for Azeroth Choppers will be rumbling its way to a vendor in Azeroth sometime after the launch of Warlords of Draenor. This mount will cost a pretty hefty sum of gold, however, so you might want to start saving up now if you want to ride around in style on this masterful machine. As a reminder, once the winning Horde Chopper is added to the game, it will be available for free to players who log in between now and September 30, 2014.
Remember, only characters of the associated faction will be able to ride each bike, so buyer beware!