I've searched the forum but I didn't found a similiar thread so I hope this is not a repost.
To be able to do this method you need:
50 skill in Enchanting.
25 level horde character.
There's a faction in Stonetalon Mountains called "Krom'Gar" which are part of the horde.
The whole questline starts in Ashenvale with the quest "We're Here to Do One Thing, Maybe Two..." Quest Link
Once you start doing their quests, you earn ranks you unlock items in their quartermaster.
The things is the items that are sold there are disenchantable and yield profitable mats.
Once you reach the last or the second last rank you're able to buy all items and therefore you can choose the cheapest one. They are all around the same ilvl so it doesn't matter what you buy.
The whole process with gaining ranks isn't slow at all and you'll be end-rank in no time.
Their quartermaster is located in the krom'gar fortress which is where you'll take most of the quests.
I found out that the most profitable item is:
It has:
78% to yield - 1-2 Soul Dust and
22% to yield - 2 Greater astrall essence
On my realm the price for a stack of Sould Dust is around 40g
and the price for a stack of the essences is 25g.
This is kinda realm dependant so check your AH prices before you start doing it.
For about 15min of disenchanting I made:
9 Soul Dust stacks - 9x40 = 360g
6 Greater Astral essence stacks - 6x25=150g
So in about 15min I made around 500g worth in enchanting mats.
I hope that method helps you, thanks for taking your time