For those who have picked up Z400's this may be another option.
I picked up four of the following servers on eBay
SuperMicro Storage Server 24 Bay 2026TT-DLRF 2x X8DTT-HEF+ CSE-217
https://www.ebay.com/itm/192395848816?ViewItem=&item=192395848816I paid $274 total for all four or $68.50 each.
These do not come with processors, memory, heat sinks or power supplies.
These systems have two independent dual processor servers in one case. Each of those independent servers can take dual Xeon 5600 series processors. So each SuperMicro Storage Server 2026TT-DLRF will have four processors.
I purchased a set of six heat sinks for $48.71 or $34.47 for set of four for one of the SuperMicro Storage Servers.
https://www.ebay.com/itm/312081078444That raised the price for one server to $102.97.
I am picking up locally four other complete "SuperMicro Storage Server 24 Bay 2026TT-DLRF" that have dual 1400 watt power supplies. Since they will run with only one installed (the 2nd is for redundancy) I will use the spare ones to power the four above servers.
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The following items are zero cost to me as they were leftovers from me buying and selling parts stripped from computer workstations and servers. I made a profit on selling those parts:
a bunch of PC3-10600R 4GB memory
four Xeon E5645 hex core processors
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The current price is $8.30 for two Windows 10 Pro digital licenses.
So my total price for one of these servers is $111.27.
These servers also come with the "Dual Slot PCIe x8 Riser Card PN:RSC-R2UT-2E8R" so I can install four single slot (or two dual slot) GPUs for additional hashing in each system.
A feature on Supermicro servers is that you can set the fans to economy mode and they are much quieter than traditional servers.
Over time I will purchase faster processors and more heat sinks to fill out the remaining systems.
I will post results when I get these systems running.