In the video below, Matt Wichlinski demonstrates how to perform an assisted natural glute ham raise (aka Nordic raise or natural leg curl). He also shows an inexpensive homemade apparatus that can be used to perform the exercise. Those familiar with this blog may recall seeing something similar here. Matt’s version is easier to build.
As for the band set-up, you could also attach the bands overhead as demonstrated at approximately the 9 minute mark within this past tutorial (link here).
As for comparisons between this floor based exercise and a true GHR machine, there certainly are differences. I’ve used both and actually prefer the low-tech variation. I do however know others who prefer the actual machine. In either case, both movements are effective. The floor based variation is typically more difficult though based on the pad angle of the machine. Keep that in mind if you decide to work with this exercise. It is likely more difficult than you initially realize.
As for additional low-tech hamstring choices, the following links provide a few options: