The weights of body armour in High Tech are off because the real items cover a lot less of the body than HT assumes. The hardened steel armour in Low-Tech would cover steel plate up to TL6 but, from TL7 onwards, some fancy modern alloys and advanced hardening techniques make steel even more protective. Today they can make steel more protective than titanium alloys of the same weight.
Cost will be lots. The raw materials cost less than in earlier times but labour is much more expensive. You are looking at around 20 thousand dollars to get a decent custom fitted plate harness made today. The one that Dr Tobias Capwell commissioned from Robert MacPherson in 2005 was estimated to be worth around 56 thousand dollars at auction a year or two later.
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