It IS available on DVD!
It can be found on the Millcreek 50 movie pack titled Nightmare Worlds along with 49 other titles that vary from great to unwatchable quality wise.
shareI got Mill Creek's Drive-In Classics 50 Movie Pack, it's got the original POTLU title though. It's an okay movie. There's also another collection set with the movie, a Sci-Fi set released by St. Clair. I can't remember the name of the set.
I got it on the 100 Movies: Sci-Fi Classics pack, the Mill Creek version. It's cropped to fullscreen, not the greatest quality video transfer, no frills, and Mill Creek for some reason thinks it's okay to superimpose "Mill Creek Entertainment" over the bottom right corner of the screen even on a DVD release. But it does indeed exist on DVD.