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Alchemy and Primal Might
Requires Alchemy (350)
The recipe is almost as valuable as the Primal Might itself, but at least its easily obtained so you can learn it yourself and also grab a few that you will resell. It's sold by 3 vendors, click here to see which one is closest to you.
Best place to farm: Auction House
Best place to farm: Terokkar Forest
Best place to farm: Shadowmoon Valley
Best place to farm: Hellfire Peninsula
Best place to farm: Blade's Edge Mountains
Farming Vs. Auction House
Image credit: Sanrya
Some of the Primals are very cheap and should be bought from the AH, like Earth, Fire and Mana usually. See for yourself which one is profitable to buy instead of farm on your realm.
Motes of Water can also be fished from Pure Water pools in Throne of the Elements, Nagrand.
Remember that Throne of the Elements is a good choice for killing too, if you don't mind waiting for respawns.
Engineers can also farm motes by hunting Gas Clouds around Outland. Different clouds give different motes, like Zangarmarsh is for Water and Netherstorm for Mana. You need a Zapthrottle Mote Extractor to extract motes from the clouds.
Making use of the Transmutation Specialization
Alchemists can choose from three specializations: Elixir, Potion or Transmutation specialization. When a xmute alchemist creates Primal Mights, a proc might happen, giving them even 5 extra Primal Mights when crafting.
This might given you even 5k additional gold per proc if Mights sell for 1k on your realm. Average price I've seen is around 300-700g. Usually no one is selling these so I can choose any price I want!