Apple is charging us $216CAD to upgrade the RAM to 16GB on imac 5K. I went to a third party website and they're selling 32GB (4x8GB) RAM for $200US. Why is it significantly cheaper to upgrade the RAM ourselves? Is there any cons of doing it ourselves? Also, could someone recommend me a 1867MHz DDR3 SDRAM that is compatible with the newest imac 5K?