Specs:
i7 4790K ($50)
9020 Optiplex Motherboard ($10)
32GB DDR3 RAM ($35)
7900 XTX 24GB VRAM ($900)
1TB M.2 NVMe ($50)
EVGA 700 BR PSU ($50)
24 pin to 8 pin adapter for motherboard ($20)
NVME PCIe x4 Adapter ($12)
Molex to fan adapters ($7)
Power button adapter ($6)
Total: $1140
Using Arch GNU/Linux (Tried installing Debian, couldn't get the AMD drivers to work properly, so I'm using Arch for the moment)
Can run Stable Diffusion, LLMs, and basically all my games at 1440p High to Ultra settings (RDR2, GTA V, Arma 3, etc.)
GPU passhtrough doesn't work for the moment, but I can still run virtual machines. This is a Haswell motherboard, which can be 100% freed in the BIOS over time when we have enough Libreboot devs who can reverse engineer the rest of the blobs. Intel ME is also disabled (theoretically, since you can't actually fully remove it). This is a build that I did for fun, in the future, I'm planning on switching to a Z690-A motherboard with DDR5(can be flashed with Dasharo firmware). If you have any questions, feel free to ask!
Some cases let you mount the GPU vertically, especially SFF cases. This would display the fans of the GPU through the glass.
I've seen some people paint their GPU backplate.