Apple has confirmed the patch upgrade fee for Core 2 Duo systems equipped with 802.11n card will be $1.99. Apple previously stated that it will charge $4.99 for the patch, however due to many negative responds Apple decided to cut the price. This patch will be available for free to those who buy the new 802.11n Airport Extreme base station. Apple released a statement regarding the reason why they need to charge for the patch.
"The nominal distribution fee for the 802.11n software is required in order for Apple to comply with generally accepted accounting principles for revenue recognition, which generally require that we charge for significant feature enhancements, such as 802.11n, when added to previously purchased products,"
Apple To Charge $1.99 To Activate 802.11n [via gizmodo]