Amazon is offering the 128GB Samsung EVO Select Class 10 UHS-3 MicroSDXC Memory Card w/ Adapter (MB-ME128GA/AM) for the best deal.
Next best price on Google is $24.99 shipped
32GB for $7.49 ($0.234/GB)
64GB for $11.99 ($0.187/GB)
128GB for $19.49 ($0.152/GB) - BEST!
256GB for $40.99 Shipped ($0.16/GB)
512GB for $94.99 Shipped ($0.185/GB)
Free shipping with $25 purchase or with Prime