I have been down this path several times, as I built ballistic helmets for me and my mates. IMHO, the Gentex helmet at 650 is probably the best deal going. I have bought ACH's and cut them down, then added all the extra doo-dads, and quite frankly unless you just really can't afford it (or really want to roll your own), you'd probably be better off just buying the damn Gentex helmet. I mean by the time you add all the rails, cover, shroud, pads, suspension, etc. you might save 150-200 bucks.
The Gentex comes standard with all the OpsCore goodness you would probably end up with anyway.
You can spend 1K on the OpscCore Maritime, or the Crye Airframe, but unless you have a high threat level for high explosives, and need the Airframe to help protect against TBI, you are paying hundreds more for cool factor.