You might also not need the Radeon WX7100 Pro, if a consumer level graphic card is enough there are sevaral options: https://wiki.raptorcs.com/wiki/POWER9_Hardware_Compatibility...
The more you’re ready to do-it-yourself, the more you can save. You absolutely need the motherboard and IBM chip, and then you can get other things like memory, storage, graphic card, etc. used for much cheaper. Only the memory is a bit special as it has to be registered, but because of that you might be able to find good deals since it can’t be used in standard desktop computers.
You can get more performance for the same price with AMD/Intel, but for those interested this platform is not that out of reach. I use it as my workstation and I’m happy with it.
Not unreasonable. $500 for the 4-core processor or $800 for the 8 core. Basically what you would have paid for a decent system decades ago, without adjusting for inflation.
That’s 8 cores, which since Power9 has SMT4 means 32 threads. The 4 core CPU bundle is a bit cheaper but when you add the 2u CPU cooler its price gets very close, so it’s not worth it unless your computer case is too narrow for the 3u (≃15 cm clearance, https://en.wikipedia.org/wiki/Rack_unit) cooler included with the 8 core CPU.
It won’t run AmigaOS unless on an emulator[1], and then you’re better off with AMD/Intel: you would lose more performance in emulating the CPU, but you would get more raw performance for your money anyway.
[1] https://forums.raptorcs.com/index.php/topic,75.0.html
If you want to run AmigaOS software natively on PowerPC your best option is a PPC Mac running MorphOS. It even runs on the PowerBook G4: https://ddg.co/?q=morphos+powerbook+g4
Or if a well-integrated emulator suits you better, take a look at AmiKit: https://www.amikit.amiga.sk/
I don’t think that this CPU would be a net advantage for those use cases. I did use Amiga computers even as Commodore went bust, hanging on, but the approach I’m going for now is FPGA implementations: https://misterfpga.org/ http://www.apollo-core.com/index.htm?page=preorder
I’m in the waiting list for Vampire4 Standalone, but for now I’ve got a MiSTeR.
So no, don’t buy a Power9 hoping to run AmigaOS on it any better than on a mainstream PC.
P.S.: the $1310.99 price mentioned by aww_dang must be from a few months ago, the current price displayed in Raptor’s website is $1732.07. Prices went up due to the current COVID-19-induced crisis, which also made Raptor cancel their upcoming Condor platform (ATX Power9 but LaGrange-based: twice the memory bandwidth): https://www.talospace.com/2020/07/condor-cancelled.html
P.S.#2: for those in Europe, Vikings (https://vikings.net/) has been trying for a while to offer them here and they might be able do so it soon: https://www.talospace.com/2020/08/vikings-upcoming-openpower...
P.S.#3: used BlackBird with 8C Power9 for sale in Germany: https://forums.raptorcs.com/index.php/topic,153.0.html