I paid around 1600 USD for everything. Counting the parts I reused from my old hackintosh, around 2000. A similarly specced Mac Pro 8-core is around 7200 USD.

thank you. A very useful contribution that neatly answers the question of why anyone would go through so much trouble. I would have guessed the difference in price was "only" a few hundred, and obviously would have been quite wrong! I never would have guessed 3.5 times!

In a way this isn’t a “similarly spaced Mac” though - it’s using Xeon CPUs, ECC RAM, server motherboard with 6 memory channels, professional GPU, etc.

The problem is if you want a Mac tower desktop they don’t offer anything with consumer components.

Well, for one, the memory is far cheaper and faster. 56GB of memory (going from eight to 64) will set you back $1,000 alone from Apple, or $252 from Amazon (and before anyone complains "but the Apple memory will be higher quality", unlikely. Same manufacturers. In fact, you can get far faster memory yourself, versus the 2666 on some Apple stuff).

But for the up iMacs (not the base models) you can put in third-party RAM. That is what I have always done to avoid Apples high prices on that (except on my laptop, where it is soldered in). But I would caution you about trying to mix in faster RAM, many non-third part. system only take one speed of RAM. That makes the system not only cheaper to build, but often you can tweak some more speed (really latency) out of it.