So i recently leveled my enchanting 1-600 on an alt, and ended with actually more gold than i started with. this isn't exactly a 100% exploit, just what i would call a pretty helpful and clever use of what already exists within wow.
When deciding to level this profession, i was level 90 and ilvl 540ish, mostly to say i had spent some time on the char doing different instances and raids. this might be especially effective for players who quested slowly all the way to 90 as opposed to quickly doing instances with heirlooms to level.
First thing i realized that more times than not, to get the mats I required for leveling, it was much much cheaper to buy items and disenchant them rather than just buying the mats you want. there are many crafted items people will price very low, and you can buy in bulk. I'm sure this is a way you can actually get a lot of gold is buying most greens on your server that are low priced, shard and re-list the items for quite a gold gain.
For the main part of the trick, well... its not really a trick, but something most people I'm guessing don't think of. use item restoration and DE everything that you had gained and vendered on the char. anything you have vendered or deleted, can be restored once a month. so after you go through all the trouble of leveling the profession, go back on and restore everything, for me it was 300+ items, and between old quest items and things i had been just getting rid of, i made well over 10k gold. im guessing i could do this on many of my other chars with the same result, making back much more than is costed to level the profession.
Once again, the main trick is to go onto blizzards website, and restore pretty much everything on the list, sharding or selling back anything you really do not want. many greens shard into mats that sell for 10-15g per mat. some level 80 greens you might have vendered might be worth well over 100g per item.
I hope this was helpful to some people.