The Cheapest Mac Compatible Thunderbolt 3 SSD - So Far
The collapsing cost of solid-state flash memory helps. Conventional off-the-shelf 2.5" SATA SSD's have become ridiculously cheap - and the trend towards high-density PCIe SSD modules / blades are even faster using far less raw materials and space. So Thunderbolt 3 SSD blade drives are appearing (or have been announced) leveraging the prowess of both technologies. We've seen LaCie introduce a $1999 Bolt 3 SSD months ahead of everyone else at a price few mortals could justifiably afford. We've also seen OWC ship their ThunderBlade(tm) 3 portable drive with prices ranging from $1199-$4999 MSRP. Ouch!
Fortunately some low-cost portable SSD ThunderBolt 3 drive alternatives came to market early. Both CableMatters and Plugable's TB3 external SSD's appear to be pretty much identical OEM devices, both 480GB in a portable form-factor with a short 6 inch ThunderBolt 3 cable integrated into the drive's case. These are shipping from both Plugable and Cable Matters with Plugable's offering currently about 30 bucks cheaper than the other. Priced just under $300 USD,they were temporarily the cheapest ThunderBolt3 SSD of 2018 and will deliver the most bang for the buck. The tradeoffs include incompatibility with USB 3.1, lack of Thunderbolt 3 pass-through ports for other devices and a non-removable cable.
OWC now sells their 'low priced' Envoy Pro EX ThunderBolt 3 SSD for Mac in either very affordable 240GB or 500GB versions. They're now on the shelves or available at online retailers.
As more competition arrives in force, downward price pressures will help somewhat. The insanely competitive USB 3.0 and USB 3.1 USB-C Mac backup drive market for HDD and SSD storage for Apple computers has become ridiculously cheap, TBolt will and always has carried a price premium for more demanding enterprise and professional market applications.