Thanks for the updated info!!
Yeah, FC3s are no longer required for crafter progression, so it makes sense that they're tanking. I'm so sad none of the new stuff uses demimateria (with trivial exceptions)I'll update the LTW note next time I update the guide. Still, 6k for an i70 item isn't that bad. You have to get up high enough to do the r115 stuff somehow.
Archaeornis Leather is so expensive relative to other new things largely because the skin is a pain to get right now. The enemies that drop it do so pretty rarely. I killed twenty and only one dropped the skin, though it did drop three. Compared to items that are mined or harvested, this is far, far slower - I obtained 60 Mythrite Sand (12 nuggets worth) in the time it took me to get 3 Archaeornis Skins (1 leather worth). The leather also takes Coerthan Tea Leaves, which appear to only be from an unspoiled node, unlike the base mats for other classes which take stuff from non-unspoiled. The easiest way to get it seems to be desynth, actually. The leaves are also needed for the next level of leather. Why couldn't they have given us seeds for the tea leaves too?No new items can be grown in gardens...
So, everyone who is an LTW desynther and reading this thread, capitalize on desynthing the belts right now before the price of leather tanks. You can get them for only 9k from vendors if the MB prices are higher than 9k. The belts are r115, can drop up to two leather, and only have one other ingredient. You should be able to make much more than they cost as you level to ~140 dSkill, just like we did with the Bridesmaid's Sandals. Just, uhh, if you're on Faerie, don't do this before I can <_<
So, it seems that the way to tell what's r115 and what's r120 for the c51 items is to look at the "Difficulty" of the craft. Items with 339 Difficulty are r115, and items with 421 Difficulty are r120. As a side-note, it seems the levels listed in XIVDB for the recipes are the "rlvl"s that I've been referring to. They have "Agate Ring of ..." as "recipe level 115" and "Yeti Staff" as "recipe level 120".