As has already been mentioned, "reasonably useful" NV gear does not come cheap...
Notwithstanding the fact that it's quite a bit more difficult to "walk" a trail in darkness using a single image tube NVG including a GEN3 one like the PVS-7 or PVS-14 due to the lack of depth perception. To have proper depth perception, one does require true binocular vision and thus you would also need dual/independant image tubes, one for each eye, in order to have equivalent capability. This is why you will see dual tubes being used by night time aviators and other "professionals" who need depth perception in the dark. Not to say that it can't be done with a single tube solution, but that walking with one over difficult terrain means you have to be more careful where you place your feet and it will take a bit of practice to become really good at it without running into things.
'Fly