I leveled my JC at the same time that I leveled the character. It is a little less expensive that way (when you mine nodes while leveling), but any way you look at it, leveling JC is VERY expensive.
First of all you are going to need a LOT of the metals, both ores and bars. Even a stack of copper bars can get pretty expensive depending on the realm economy and can go anywhere from 2g-20g per stack. Sometimes more. The higher you go in the metals hierarchy, the more expensive stacks get. Ore is usually even MORE expensive, as people will frequently buy ore to level mining AND JCing. Ores can also be prospectable, destroying a stack of 5 ores to randomly generate a gemstone or two. So if you're short on gems and the AH doesn't have any more (which frequently happens), you may need to buy stacks of ores just to get a CHANCE of getting the specific gems you need. This is VERY costly.
You will need a LOT of gems, which can be extremely pricey on the AH. I'm leveling my petopians hunter as a JC right now, and even buying the first tier of gemstones--malachite, tigerseye, and shadowgems--can be as much as 1-2g per gem. It doesn't sound like much, but when you need 2-5 of a gemstone per JC point, it starts to add up. Especially when you get to the more expensive gems further down the line, which are rarer. I need Jades right now, for example, and those are going 10-15G a pop. But I need 2 jades per point, which means it is going to cost me at LEAST 20G per JC point, not including the cost of the metal bars/ore I needed to use.
It is very easy to blow a LOT of money--I'm talking 100-200g--on just 5 points in JCing to get to the next selection of JCing choices at your trainer. And that is with stored up mats, such as metal bars you've stored a way or gems you have hidden in your banks. My advice is to CERTAINLY have a miner to help you with this. Even doing a round or two of a zone to get a few stacks of ore will help enormously.
Either way, be prepared to lose a LOT of gold. Especially when it comes to rare gems that aren't on the AH a lot.
Also, keep in mind that the payoff isn't going to be immediate. Some rings and necklaces can sell decently well for their level, but I find most of the time there are SO many of the low-level JC items up on the AH that they're worth next to nothing. The REAL payoff is going to come with gem cuts when you hit 450, so remember to be patient! You will also need to donate a lot of TIME to JCing too, as it's one of the only professions with its own daily, and each daily earns you the tokens that you will use to buy epic designs.
Hope that wasn't too long. Good luck
~VelkynKarma
I've just started a JC too, and glad he'll be funded, and that my main saved all those stones and gems in the bank.
You can try Dalaran or Shattrath though, if you can get ported there.