While I'm too old to have seen the end product, I was always impressed that those developing EFA made an effort to speak to other aircraft project offices who were working on new helmet designs. I recall British Aerospace coming to see us in 1995 on noise reduction, and to Lynx on 360 deg audio warnings. Very often helmets are an afterthought. £35k is a little more than a Mk4 (!), but I assume they followed suit and all helmets are now made-to-measure. In 1996 a basic Mk4A was about a grand. M2M increased that a little, but in practice the travel and subsistence to the factory cost more. Decent transducers would add about £3k. Price soon builds up.