http://www.streacom.com/news-item/the-open-benchtable-project/
EDIT 12 November 2016: updated version:
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While technically not a case, I feel this is pretty SFF right there, with it's insanely focused and optimized design. You can attach the PSU through holes in the feet, the two slots can house screws when in use and be used as 2,5" or 3,5" mounts. I'm hoping this will be below 50$.

EDIT 12 November 2016: updated version:

END of EDIT


While technically not a case, I feel this is pretty SFF right there, with it's insanely focused and optimized design. You can attach the PSU through holes in the feet, the two slots can house screws when in use and be used as 2,5" or 3,5" mounts. I'm hoping this will be below 50$.
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