Other than building it yourself from parts from some electronics store, you will not get the same quality parts apple uses nor will you be able to meet the same specs with the same capabilities - case in point: the new Mac Pro (comparable very high end boxes will cost $160K and still not be identical nor will any other box drive 6 6k monitors simultaneously with no lag); same quality for the new lower priced less capable Apple boxes.
I wouldn’t go quite that high. . . Some MIGHT reach $160,000 if fully populated with all the stuff required that will fit in a fully populated Mac Pro. . . But then that Mac Pro would be in the $40,000 range itself. Of course you can add 36 devices onto the Mac Pro through daisy-chaining the Thunderbolt 3 ports at 40Gb speeds, and not lose anything. . . Including storage, more graphics cards, more monitors, even more Mac Pros. There are rack-mounted Mac Pros that can be chained together to create a Supercomputer of any size, if you desire. . . But then the 56 teraflops of the fully populated single Mac Pro is no slouch in computing power.