I'll talk about ballistic helmets.
If you want ballistic protection, and don't mind the price, the Crye Precision Airframe is the tits. 2.6lbs? It's a LOT lighter than the PASGT or the ACH, I don't know if they used carbon fiber nanotubes throughout, or if it has Kevlar too, but the inside is carbon fiber. It's also lighter than the Ops Core helmet, costs less, has more coverage on the nape, more upgrades (if you want those) and ventilation on top. Only ballistic helmet I know of that has that. Has the side rails and shit for eye pro, ear pro/commo mounts, lights, cameras, etc., and they make a nice multicam cover for it too. The pads are comfortable and the straps lock it down tight on your head. I sure wish I had that when I was in. Now that I don't "need" it, I have it. Isn't that how it always works?
That helmet is about $844 on TNVC, but for a few hundred more than the Exfil, ballistic protection and only about 1lb. heavier, I'd go, and did go, with the Crye. Even if I don't need ballistic protection, I have it and for a very minor weight gain. If you want just light as possible with no real protection, then those modified rock climbing helmets (less than $100 bare?) may be the way to go. Just get a better mount if you get a cheap helmet, and don't skimp on the pads and chin straps either. All that is what makes it solid.
But shit, if you don't need a helmet really, have you considered some of the new "skull crushers"? They aren't exactly skull crushers anymore, they are quite comfortable from what I'm told. I'd like one, and may still get one. But for over $300, I gotta think it through. It would be nice for just walking the woods wearing a boonie as opposed to a helmet.
My rig is as follows:
Crye Precision helmet w/rails, cover and bungees.
Norotos INVG mount.
Norotos Dual Dovetail for PVS14.
Ops Core VAS shroud.
I have a PVS14 now, but may go with BNVD's or even GPNVG's one day, or possibly the PSQ-20 (if I can swing it!).
I'm gonna add for sure one of those tethers they make now. Much more compact and nicer than all the 550 cord.
I wanted rock solid and I got it. I hated the damn Rhino mount and J-Arm. If you can't swing the helmet and a better mount, then I'd get the helmet and the VAS shroud and use your Rhino for now (TNVC says the Norotos Universal shroud is better if you don't mind the price). Your Rhino will work with the VAS or the Norotos Universal or the Wilcox shroud (very similar to the VAS). Then later, look into the INVG or other Norotos or Wilcox dovetail mounts. Wilcox makes the new Army mount, better than Rhino, but still uses the old J-Arm --it's worth the about $200 extra for the better dovetail mount. Wilcox is lower profile and likely better for 14's, but if you plan on getting BNVD's or dual tubes later, the INVG is likely better IMO.
If funds are an issue, then just suck it up and get the 3lb.+ Rabintex or other make ACH-3, the one with the ears cut off. It's damn nice too IF you get good pads and straps. Rails are also available. For about $500+, it's less than the Crye Precision, and you'd be better served with that helmet and a better mount like the Wilcox or Norotos dovetails. Any of those dovetail models are good, just pick the dovetail model you like best. If you like the Rhino though, then look hard at the Norotos AKA2 or TATM and a Wilcox dovetail J-Arm. Then you'll have a good ballistic helmet and a good stable mount.
Trust me here, you don't want a shitty mount using a shitty J-Arm with a shitty helmet with shitty straps. If so, you better have some 100mph tape handy. You could ask me how I know, but I think you get the idea. Bottom line is NODs are more enjoyable and useful when they don't wobble around a lot.
Also, call TNVC. They'll help you get what you need without selling you junk or over-selling you. I really have lots of respect for those guys and they'll take care of you.