http://www.ign.com/articles/2014/06/10/e3-2014-gamecube-adapter-controller-and-smash-bundle-pricing-revealed
Nintendo unveiled pricing details for a group of Smash Bros. related peripherals today.
The GameCube Controller Adapter for Wii U, which supports up to four GCN controllers (including WaveBird), will be available for $19.99 USD.
Nintendo will also sell Smash Bros. branded GameCube controllers for $29.99 USD each. Lastly, a special Smash Bros. for Wii U bundle, which includes a copy of the game, one adapter, and a GCN controller, will be sold for $99.99 USD.
All of the Smash Bros. related products will launch the same day as the Wii U version this Holiday 2014. Nintendo announced earlier today that its figurine platform, called amiibo, will also launch the same day as the game.