Building a 16 thread cruncher

[Dirk Broer]

But how much for a 16-thread Threadripper, Jack?

Perhaps unsurprisingly, the motherboard of choice is from Asrock again: an ASRock X399 Taichi can be bought for $339.99 at Newegg and is the cheapest TR4 board there, as it is here in the Netherlands too.
RAM-wise we can do with the same as for the Ryzen 7 board, while a Threadripper 1900X costs $549.99

So: $339.99 + $299.99 + $549.99 = say $1190 and your entry-level Threadripper (using some spare parts from older systems again) is ready to go, and can be significantly improved over time.
The outcome of this sum even surprized me! It's comparing high-end Ryzen 7 (on a low-end board) to low-end Threadripper, but I hadn't expected it to come out so close.
If you want to compare the Threadripper setup with a comparable Ryzen 7 setup, you can take the Asrock X370 Taichi and add $135 to the price of the Ryzen 7 system.

The Ryzen 7 system has (when using the Ryzen 7 1700 of 65 Watt TDP) a much lower TDP than the Threadripper system with its 180 Watt TDP CPU, but the only thing you can do to add more performance to that platform is buying the 95 Watt TDP Ryzen 7 1800 or 1800X (or wait for a 10- or 12 core to arrive on the AM4 platform in the future). The expandability of a Threadripper system is much bigger, and on top of it you get more PCIe lanes. Nice to know is that the 16-core Threadripper 1950X still has the same 180 Watt TDP and as such is a much better buy than the 1900X.