The Elementium shuffle has already begun.
Within the first 24 hours of Cataclysm going Live, prices on Auchindoun for Elementium have gone down from the 550g/stack I was selling them at to 100g/stack, which is almost the price one would expect Elementium to stabilize at once the dreaded "Cata inflation" is properly taken into account. The reality is I am finding it entirely possible Elementium will reach near-Saronite levels within the next month based on its ease of acquisition in Twilight Highlands alone - I am talking in the neighborhood of 40-50g a stack. Unlike Saronite, Elementium Bars vendor for only 7.5g/stack, which means its price will only be buoyed by the Shuffle itself, which is great news for us.
Speaking of the Shuffle, if you have a Jewelcrafter and are not buying Elementium Ore at 200g/stack, you are probably giving gold away; at 100g/stack, you can literally buy 200g with 100g. The new uncommon gems should be going for 50g apiece minimum, and likely quite a bit more given their necessity for leveling JC. It takes 475 JC to prospect Elementium, so you will have to either start buying said gems or prospect some likely more pricey Obsidium Ore to get to that threshold. Once there, each stack of Elementium Ore is four uncommon gems minimum, which means you hit a profit at any point you get an extra gem (possibly a rare!).
Incidentally, the uncommon gems vendor for a whopping 5g apiece, which sets their deposit fee at a ridiculous 3g 30s whereas rare gems vendor for less (3g). The irony here is that none of the uncommon gems are useful in of themselves* since they require ilevel 285 gear to be socketed into, and there is basically zero gear rewards until the endgame that even have sockets. The uncommon gems vendor for 9g apiece when cut, so to a JC the True Vendor Price of Elementium (and Obsidium) Ore is 36g a stack minimum, although you can probably bank on 45g.
*Obviously the gems are good for leveling JC and making jewelry to be disenchanted. Uncommon gems are also used in Alchemy for transmuting 3 of the same color gems plus some herbs into the rare gem of that color, i.e. Transmute: Inferno Ruby. And, of course, to transmute the one-size-fits-all metagem. One additional thing to keep in mind: these gems transmutes have no cooldown. The herb cost is basically immaterial, so the rare gems should always be pegged at uncommon gem price, e.g. Carnelian x3 = Inferno Ruby.