Most of the enchanting mats coming into the market are going to be from people who craft items to disenchant. Disenchanting weapons yields essences 75% of the time and dust the rest of the time. Disenchanting armor gives you the inverse, yielding dust 75% of the time. Without any doubt, the best item in the game to disenchant for Celestials right now is Carnelian Spikes. It's ilvl 317 and takes a jewelcrafter nothing but three Carnelians and three Jeweler's Settings, available for 1.05g at the vendor (assuming guild perks and rep). It's not only the best item to craft, it's the only one on the list. All other green weapons are drops or quest rewards, and all the blacksmithing craftables are blue or purple.
The issue with disenchanting spikes is that the opportunity cost for these mats is an Inferno Ruby through an alchemy transmute. Every single Carnelian that gets used to make Celestials is not being used to make Inferno Rubies. Most players capable of making either will decide which path to take based on what costs more. If Celestials cost 90g and uncut red gems cost 130g, it's always worth making the red gems until you push them down to the price of the Celestials. You have to ensure that you include the values of Heartblossom (used for the transmute), Hypnotic Dust (a byproduct of the spikes), and transmute mastery (20% bonus to gems produced).
The other factor to remember is that the only way to get Carnelians is to prospect Cataclysm ores. This will yield green-quality gems, including Carnelians, in equal quantities. To get a stack of Carnelians, you will also have to deal with a stack of every other color of gem. Several of these can be turned into low-level green armor that can be disenchanted; however, this will yield mostly dusts. Also, Zephyrite can't be used for anything but selling to non-prospectors when the JC daily quest calls for it. We used to vendor it, but since patch 4.2, this is no longer worth it unless we need to bag space now.
Actually, these greens are the reason that Hypnotic Dust is so much more abundant than Celestials; each of them has a 75% chance to yield dust, and while the guild perk Bountiful Bags does proc on dust (as well as blue or purple shards), it doesn't proc on essences. For every green weapon you make, you'll be making 7.5 rings/necklaces and vendoring three Zephyrites. It's still more Celestials than, say, making the Darkbrand Helm or Spiritmend Robe, as these produce dust at about the same ratio as the green jewelery.
Of course, a significant number of enchanting mats enter the market through 5-mans. I routinely see 10 or more drops from trash mobs between bosses while farming valor points, and more often than not, there's an enchanter in the group that gives us the ability to DE. There are 162 weapons on the drop table and 347 armor drops on that same table. This leads to a much better ratio of Celestials; however, it's not controllable. This means there will always be a background supply of Celestials that scales roughly with the number of dungeons being done on average by people in your realm.
Right now and until the demand for enchants on new gear gears down to a level that it's matched by the supply of new enchanting mats, Celestials are going to be expensive and in short supply. People are already running more 5-mans so they can buy their new valor gear, but on many realms, there is less mining happening. The only way you can proactively create Celestials is through ore, so keep an eye out and buy when there's large amounts of supply.
Also, if you calculate that on your realm Inferno Rubies are still a better use of Carnelians than making Celestials, it might be a good idea to buy all the Celestials below the price where it would make sense to make them instead.
If you elect to set that as your target, make sure that you pop online as often as possible to pick up any mats posted below that, and when you're calculating whether it's profitable to sell a scroll, use that value for the Celestials rather than whatever your addon tells you. Also, if you ever see raw Carnelians for sale on the AH at a price that would allow you to make your mats at your target price, buy them up and make them into mats.
These strategies can help a scroll-making enchanter get through a patch; however, they stop working when the new stock catches up to the demand. If you notice your scroll sales drop and there's a large increase in the availability of enchanting mats, consider forming an exit strategy. Sell as much of your stock as you can so you're not caught with a large inventory that you have to reassess the value of in order to sell.
Hypnotic Dust is currently almost a byproduct of disenchanting. This leads to massive levels of supply that really force the price down. It's certainly used by enchanters, but not as fast as it accumulates. If you have a tailor, you can try "venting" excess dust into the bag market with Embersilk and Otherworldly bags, but that's a much smaller market than the enchants. I suspect we'll be seeing some sort of dust sink from Blizzard soon.
Maximize your profits with more advice from Gold Capped as well as the author's Call to Auction podcast. Do you have questions about selling, reselling and building your financial empire on the auction house? Basil is taking your questions at firstname.lastname@example.org.