IMHO, the Virtual Research Flight Helmet was, and still is, the ultimate head mounted display, except of course, it needed modern high resolution LCD panels. Otherwise, it had incredible field of view, great ergonomics, and unbeatable LEEP optics. I came across a more complete brochure including the retail price list (starts at $6,000.)
One unusual aspect of the Flight Helmet was that the left and right images don’t completely overlap, producing a wider image than the normal 4:3 aspect of NTSC video. If you wanted 100% overlap, you needed to purchase prisms (3M Press-On Fresnels) to shift the images horizontally into alignment. To run the helmet monoscopically, the prisms are a must!