I done some testing for other reasons, and was developing the Smithing skill with iron and leather. It seems that Iron daggers are still, "the best bang for buck", as far a s material. I was testing for something else so I could be mistaken. But just from having the materials in hand and watching the bar go up, it appeared to be close. The number of IDs to craft is up there. Before it was 475, now it's over 2000.
I could have used other materials, but iron and leather was easy to manage.
Helmets seem pretty efficient. Leather helmet, for ex.... 2 leather, 1 strip. 60 value. (let's see.... ok, yeah. Double checked on the wiki. Iron dagger is 1 iron, 1 strip. 10 value. Iron helm is 3 iron, 2 strips. 60 value. Slightly less than 3x ingredients, 6x value; Steel is better. Helm - 2 steel, 1 iron, 2 strips... 125 value. Dagger 1 steel, 1 iron, 1 strip... 18 value. Less than 2x ingredients, 7x value.) Helmets tend to have about the same low ingredient cost as boots & gloves, but 2-3x the cost.
(And then there's doing any gold & silver jewelry you happen to get the mats for. But that's looking at it from the standpoint of using found materials, not Waiting them out from the vendor.)