Not only is the exit fee not expected to only be $10M, but the Big East is charging an entry fee. From the Courant:
Some financials of the situation became clearer Monday. Sources told The Courant the exit fee from the AAC could be as high as $12 million because UConn would not be giving a full 27 months notice. The first payment of $2.5 million would be due once UConn notified the AAC of its withdrawal. The Big East entry fee is believed to be about $2.5 million.