Say what you like about Apple, as a company it's not exactly on the forefront when it comes to offering standard connectors for peripherals. Case in point: the latest iMac revisions lack eSATA, something of a bother for companies that make external storage devices. Companies like OWC. So, that particular organization is introducing a service to add that to 27-inch iMacs, cutting a small hole into the bottom-right of the display and sticking an eSATA port behind it. It's a nice idea, the results look flush enough, and 48-hour turn-around time is great -- but $169 is hardly small change. You can, however, take that time to get a 480GB Mercury Extreme Pro SSD stuffed in there as well for a mere $1,649 more.
AppleiMac 27-inch with Retina 5K display (late 2014)