Buy.com offers the Kingston 16GB Wi-Drive WiFi Storage for Apple iPad, iPhone, and iPod, model no. WID/16GBZ, for $99 with free shipping. At $6.18/GB, that’s the lowest total price we could find by $3. The Wi-Drive provides an additional 16GB of media storage, via 802.11n connectivity, for an iPhone, iPod touch, or iPad. It can be shared with up to two devices at once.
Amazon has it for a buck more.