B&H has the Sony 64GB UHS-I Speed Class SDXC card for $27.50 (reg. $38.30) through April 29 (tomorrow). The Speed Class 3 rating means that it is capable of recording 4K video in current cameras like the Panasonic GH4 that record on-board 4K video. You can learn more about Speed Class ratings and other SD card specs in this article – Demystifying SD Cards.
Additionally, several other Sony memory cards are on sale right now. Check them all out here at B&H Photo.
Note: This is labeled as a gray market item and, therefore, won’t include a US warranty card. At the time of this post, ebay seller Deals-All-Year has a positive feedback rating of 100% and offers its own 1-year parts/90-day labor warranty with the camera.