Refer to this thread: Will the 2016+ NC750X's LED headlamp fit an American 2016 NC700X?
Also this one: Will the 2016 led headlight fit the older models?
I haven't yet seen a US spec NC750X parts listing, but I'd expect the cost of the 2018 headlight assembly to be $350-400 discounted.
Although it's a different model, it's interesting to note that the Honda NC700JDAC NM4 Vultus headlight assembly has a list price of $1,009.78.
I just saw the USA version 2018 NC750X parts list at cheapcycleparts.
The headlight mounting stay, 61318-MGS-D30, is the same part number as on a 2016 NC700X, which is also the same as on a 2012 model.