My apologies to the moderators if this post violates any rules; feel free to delete. Anyway, for about $100 I've built a homemade glute-ham raise that I'm incredibly proud of, and have included a breakdown of exactly what you need for parts in the current issue of the small bodybuilding/fitness magazine that I produce (though the article doesn't include step-by-step directions, anyone that can use a power drill should be fine). The contraption allows for reps to be done from the parallel to the floor position, though I might be adapting it soon to allow for a full back extension, too. I don't think it's appropriate to advertise the magazine here, but shoot me a message at TheNaturalPhysique@gmail.com
if you're interested. Check out the image I've attached for a better idea.