This is the only correct answer. There are higher supply (seeing as this is a game where everyone can do everything) so prices are lower.
However in places like Gilgamesh.. everything seems to be 3x more expensive than on something like Cactuar(probably an exaggeration..) but everything on Gilgamesh is suuuuuper expensive. So maybe that isn't an exaggeration. Dyes are almost un-buyable or probably simply undesirable to someone with limited gil. Its just too expensive. Everything.
Thanks all! Some great answers here I didn't think about.
Now that I think about it on my Legacy server there are tons of Max Level Crafters (most of the Max Crafters I remember from the early days). It makes sense that if Legacy servers have so much competition it drives down prices.
(Same for Max Level Gatherers I suppose.)
And, yah, on Masamune at least there is very little RMT spam (it used to be hard to create a new character on this server as well).
Jpn servers in general are cheaper, being the game is super popular and NEET culture. 15HQ adamantine nuggets on Alexander JP only cost 60k, while on Hyperion its would have been 150k (almost 2x for a basic mat)
I actually adopt the legacy mindset when it comes to pricing things on the boards. 10K is a reasonable amount for a level 20 to spend on a high quality piece of gear. 15K is a reasonable amount for a level 30 to spend. And yet I routinely see idiots trying to charge 40-50K for a level 15 item. I mean, it's not like you can't makes those items for 500 gil from a vendor. Take your 500% gil markup and be glad for it.
It is partly server population (you can't make a character on a legacy server, only transfer to one so these servers aren't getting more people like other servers do) and partly server mentality. In the case of Gilgamesh, that is -the- prime raiding server in the NA pool. It's the main server for the world first race we have here, and because of that not only do people tend to have more gil but they're much more willing to spend large amounts on things top help them prep for or gear up to those races. Because of this people are going to take advantage and sell at higher prices.