If some of the components are sourced used, then the price for this could easily be <$1000 for the core components, though you could make this cheaper with a different CPU and GPU, cheaper memory, see below:
(prices estimated from eBay)
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CPU, fans, cpu cooler, motheboard, RAM, PSU, GPU (comparable Radeon 280x)
$865 +/-$50 (shipped)
Note: a cheaper CPU (+overclock), a different PSU (500-600w would be fine for this system), cheaper ram (+overclock) would net a $100-200 savings for nearly identical performance
Case (Silverstone fortress FT-03)
$200 est
Apple-compatible PCIe wifi card
$130 shipped
Storage, speakers, mouse/keyboard, and display vary by user needs the cost here could be $200 or less for cheap/used components or $10k for color-accurate panels, audiophile speakers, custom mechanical keyboard, multiple PCIe SSDs, etc, etc
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TL,DR - let's assume you're will to source some used components and go the cheaper route on a few things. You already have access to a screen, input devices, and speakers. In this situation, you could build a comparable machine for under $1000 + the cost of whatever storage SSD/HDD you need. You could stay under $1000 for the whole build if you opt for a cheap case and a single SATA-based SSD.
I would suggest this card, it should work, it is SATA based as opposed to NVMe. I have installed a few of these in on several older systems (x58 based and others) and saw a very large performance bump, even versus SSDs connected via aftermarket PCIE SATA-3 controller (running at 500-550mbs). YMMV if attempting to clone an existing drive - I have had this problem with add-in PCIE cards, older motherboards, and various operating systems - a fresh install to one of these drives will likely be easier.
I have been reading Damn Interesting for over a decade now. It is one of the few unblemished places on the internet when it comes to well-written, fascinating articles (possibly the only one now that isn't either riddled with clickbait or beholden to some larger business/media entity).
Granted, updates are generally infrequent, but the consistent (high) quality of the writing for over 10 years is a pretty amazing feat. Much respect for all the DI authors/contributors.
Echoing the comments from others, My "main" pc is about 7 years old running the x58 platform (socket 1366) - it easily outperforms my work-supplied development laptop.
For the uninitiated, the ebay workstations mentioned are typically these ancient x58's. Most support hex core xeons, 24gb ram (or 48gb unofficially, more on server boards and some workstations), and a pile of PCI-express lanes. As such, you can easily add in PCI-express m.2 SSDs, USB 3/3.1, and GPU's to your heart's content. The takeaway is that old pc tech can be had at a fraction the cost of new hardware with comparable performance.
I understand the marketing nonsense from Apple, the "PC does what" consortium, and hardware vendors on the whole - but there is nothing sad about owning an old pc. The reality is that the best performance for the price lies in "obsolete" platforms.
(prices estimated from eBay)
------------------------------
CPU, fans, cpu cooler, motheboard, RAM, PSU, GPU (comparable Radeon 280x) $865 +/-$50 (shipped) Note: a cheaper CPU (+overclock), a different PSU (500-600w would be fine for this system), cheaper ram (+overclock) would net a $100-200 savings for nearly identical performance
Case (Silverstone fortress FT-03) $200 est
Apple-compatible PCIe wifi card $130 shipped
Storage, speakers, mouse/keyboard, and display vary by user needs the cost here could be $200 or less for cheap/used components or $10k for color-accurate panels, audiophile speakers, custom mechanical keyboard, multiple PCIe SSDs, etc, etc
------------------------------
TL,DR - let's assume you're will to source some used components and go the cheaper route on a few things. You already have access to a screen, input devices, and speakers. In this situation, you could build a comparable machine for under $1000 + the cost of whatever storage SSD/HDD you need. You could stay under $1000 for the whole build if you opt for a cheap case and a single SATA-based SSD.