According to GameStop.com the Transformer Prime will release on December 9th. GameStop has the tablet on preorder for $539.98 for the 32gb version which is actually $40 more expensive than you can pick it up for at Amazon.com
The extra $40 is to pay for the GameStop controller which gives you access to GameStop games and more on your new quad-core tablet.
According to a story published earlier the GameStop controller will give the user access to 7 free games off the bat and they are supposed to be of console quality. From there the user will have access to even more games as GameStop builds up their cloud based gaming model.