Answer to: Make Own Fusion Drive on Late 2013 27" iMac?I don't think it is cheaper to do it aftermarket. However it is possible to do it if you "forgot" to order by the time of purchasing. All you need is a PCIe flash drive (plenty available on ebay, pricy though. OWC about to launch anytime soon an alternative), the ones that fits are those pulled from the macbook pro retina late 2013/14. Get it installed (guides available in ifixit) and then create your own fusion drive (logically combining the PCIe flash drive and an existing internal HHD/SSD), plenty of guides out there (a couple of terminal commands). I've done it in a late 2013 27" iMac with a factory 1TB HHD and a 256GB PCIe flash drive (from the macbook pro retina late 2013/14). I love how fast it is!