Today even crappiest old PCs that you can fish out of a dumpster are already new enough to have Rust/LLVM support. We have mountains of Rust-compatible e-waste that you can save from landfill. Take whatever is cheapest on eBay, or given away on your local FB marketplace, and it will run Rust, and almost certainly be orders of magnitude faster and more practical than the unsupported retro hardware.
Using actual too-niche-for-Rust hardware today is more expensive. Such machines are often collectors' items, and need components and accessories that are hard to obtain, or need replacements/adapters that can be custom low-volume products.
Even if you can put together something from old-but-not-museum-yet parts, it's not going to make more sense economically than getting an older-gen Raspberry PI kit or its Ali Express knock-offs (there are VGA dongles more expensive than some of these boards).
It's fine to appreciate SGI and DEC Alpha, have fun using BE OS, or prove that AmigaOS is still a perfectly fine daily driver, but let's not pretend it's a situation that people are in due to economic hardship.