I do not know whether this is a glitch or mentioned somewhere else, but Best Buy has a ton of 4k SteelBooks on sale - as low as $14.99, ($20 off), on most Disney titles, and others.
Amazon is having a buy 3 for 2 sale on a lot of stuff. I tried to filtered to show just blu rays and 4Ks but that didn't seem to work. You can filter yourself using the link below.
Solid Metal Nightmares: The Films of Shinya Tsukamoto (Tetsuo: The Iron Man / Tetsuo II: Body Hammer / The Adventure of Denchu-Kozo / Tokyo Fist / Bullet Ballet / A Snake of June / Vital / Haze / Kotoko / Killing)
$72.99 (was: $99.95)