I was biochem before I switched to armormech to make the crit bracer and belt. It took about 300k spent to level armormech to 400 just solely sending out companions on scavenging missions. Took about 1 day to do so (crafting non-blues only takes about 2 minutes a craft, with 5 companions it goes quickly). It took about another million in mandalorian iron (stuff is 10k+ per on my server) to get the belt critical, I hit bracer first try and belt on 10th but I've heard of people doing 15+ belts with no critical.
Leveled biochem again today, total investment has been about 1.6 million.