AMD Ryzen Threadripper 1900X has released officially now at $549. Comparatively, the CPU costs only $50 more than a AMD Ryzen 7 1800X, but it is the rest of the hardware where Threadripper 1900X configuration becomes expensive.
This price jump of $50 is not sufficient for you to create a Threadripper based desktop PC. You need to add other expenses, as such motherboard, RAM, PSU. This is where AMD Ryzen Threadripper 1900X will cost you way more than a AMD Ryzen 7 1800X.
Both of the technologies are for different set of users. AMD Ryzen 7 1800X processor is more concentric for gaming purpose applications. While, Threadripper based CPUs are better designed for content creation, multitasking program applications. For the sake of argument, check out the graphical comparison between Threadripper 1900X and Ryzen 7 1800X.
If you look forward to spend $549 so as to buy a Threadripper 1900X, you need to calculate the price of its required hardware in the total equation. All in all, the X399 motherboard, at which a Threadripper processor sits, will alone cost you $349. Since all this hardware has made debut in the market recently, you are less likely to find it at lowered price.
Where as, if you look forward to buy a AMD Ryzen 7 family processor. You can settle down and build a machine with less expenditure than Threadripper. The minimum price tag on motherboard at which Ryzen 7 1800X sits, will cost you $150.
Regardless of $50 difference between a Threadripper 1900X and Ryzen 7 1800X, analytically, if you look at the scenario, Threadripper family becomes much expensive when you add the prices of necessary hardware in total equation.