You may have this problem: i just reached lvl 40 and im having trouble making some cash. mining mithril doesn't put bread on the table anymore and im 50g short affording my mount. so what im trying to find out is, whats the best thing i can farm at my lvl that makes more money then mithril? a few weeks ago a stack of mithril use to go for 15-18g for me easy. now im lucky to get 8g per stack. its still alot but not enough.
The problem is you didnt save money beforehand, at level 27 my shaman has 127g.
How? you sell EVERY SINGLE THING YOU FIND. Trust me, it works. Is it a grey? vendor it, even if its worth 50c, its 50c more to your money pot, and if you argue "But they take up bag space!"; yes, they do, throw them away if you have more important things to grab or keep, but keep them otherwise, like I said, even 50 copper is 50 MORE copper.
Is it a white? then most probably it is of use to someone (with the exception of white armor and weapons, people tend not to buy those). Put it up on the AH for a reasonable price and sell sell sell. You know whats an amazing money maker? fishing and cooking. Even if you dont cook, selling the mats for it is profiting, Ive seen 5 clam meats go for 1-2g, and they take about 6 minutes to farm at nagas in Ashenvale.
You just have to find what people buy most, and farm it. while on your trips, mine EVERYTHING, every single node. I dont care if its copper, mister, thats another 2g you will get if you get a stack of it.
And the most important and most easy thing to do: DONT BUY CRAP ON AH ALL THE TIME.
Even if that green looks ub3r to you, it may give you a negligible bonus, but a huge dump to your gold income. As a personal tip, I dont buy greens over 1g 75s up to level 30, 2g50s up to level 50, and 4g up to 70.
Blues can vary, but make sure they are a no-no, at all times. They cost way too much and normally (actually MOST of the time) an instance blue is better, or even quest loot.
Good luck, and may your pockets never be empty.