I would imagine the 400K is for the entire system, rather than just the helmet itself. IR LED's are a dime a dozen, but to integrate them into an entire system - cockpit sensors to detect their orientation, the computer and software to translate that orientation into a "look direction", and the external cameras to make the body of the plane invisible to the pilot - all those things, and their integration together, are going to push the price tag up significantly.
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“Trouble rather the tiger in his lair than the sage among his books. For to you kingdoms and their armies are things mighty and enduring, but to him they are but toys of the moment, to be overturned with the flick of a finger.”
― Gordon R. Dickson, Tactics of Mistake
― Gordon R. Dickson, Tactics of Mistake