So, as a frugal person, I quickly realized that the cost of the materials is usually less than the cost of the finished product. Case in point, Stormleather Sash.
I purchased this belt about 3 weeks ago, 2 weeks after Cataclysm had come out. The pristine hides were 900g each, the Blackened Dragonscales were fairly cheap at 10g each. The 25 volatile water was around 10g each, but the 25 volatile air was 25g each.
Let's do the math: 900*3 + 10*10 + 25*10 + 25*25
This comes out to 3675g, and I "bought" the two Chaos Orbs for 1,500g each. Now, 3 weeks later, it's currently on the Auction House for 12,000g. This is despite the fact that the cost of the materials keeps dropping.
Let's look at Enchanting, though. Say you want a mid-level enchant for that mid-level blue piece you just picked up. Maybe you don't have the gold for the highest tier enchant, or maybe you don't want to spend 3,000g on the high tier enchant for a heroic blue item. I can't say I blame you.
Say, instead of "Enchant Cloak - Greater Intellect" (9 Hypnotic Dust and 4 Greater Celestial essences - a materials list of approximately 335g), you choose "Enchant Cloak - Intellect" (6 Hypnotic Dust - around 90g). Great, so you buy the dust off the Auction House, and post in Trade that you're looking for an enchanter.
Not so fast.
Did you check to see if there was a Vellum on the Auction House first? No? Well, I just did, and there are vellums up there for 5g. -5g-.
This is because everyone is leveling their professions, and they are willing to move the enchants at such a low price to just make some gold back, not even looking at the economic side of things.
This is also a great opportunity to make gold: some of the Best in Slot enchants are going for half, if not less, of the cost of materials. Buy those up, and a few months down the road they're sure to rise in price as the demand increases due to people raiding, and the supply decreases due to people being done leveling their professions. Of course, we have to be aware that the cost of materials may (and most likely will) decrease over time.
-Always check the Auction House for the finished product
-Possible to buy pieces for less than the cost of the materials, and resell for more later on.