Adorama offers the Crucial 16GB PC3-12800 DDR3-1600 204-Pin Mac Laptop RAM Kit with two 8GB SO-DIMMs, model no. CT2K8G3S160BM, for $89.99 with free shipping. (Amazon, B&H Photo-Video, and Next Warehouse offer it for the same.) That's the lowest total price we could find by $10. It features a 1.6GMHz clock speed.