The best way to even get near the gold cap is multiple processes....
Step one: level as many characters as you possibly can, get them all to 80. while saving all the gold you have accumulated except for the basic travel/training. making sure to do minimum instances.
You will spend each character around 1400g on just travel. and training even more. You could do instances up to around outlands level. besides those things do not spend gold.
Step two: spend the gold you have made on leveling the characters, on power leveling (farm if possible save gold WHEREVER YOU CAN) professions. get the basic, Herbalism, Skinning, mining, Alchemy, Enchanting. the others are useless when it comes to making gold at large levels.
Step Three:
-Sell herbs the low level herbs make more than the regular WotLk But, you can herb the high level herbs faster than you can the low level. if possible get as many "frost Lotus" as possible.
-Sell ore.
-Sell leather.
Step Four: Do dailies on every character that is level 80. paying special attention to the higher paying dailies, such as ones in Snow Peaks and Ice Crown, avoiding those in Grizzly Hills. send all gold made to a "bank toon" to avoid spending.
Step Five: Once you have made around 6000-10,000 gold. Its time to work the auction house. buying out ALL the items that are the most popular at the moment. And then when people are desperate for the item, you put them in at high prices. You can raise the prices on items, and end up getting more. Another way to do it, is to buy all the low priced items of one thing, and make sure yours are always the lowest. but have that price be high. You end up raising the price, and getting a bigger income. This is very risky, but the fastest way to get gold.
Step Six: do a combination of all these. putting as much time in it as possible to gain the most overall gold income.
Step seven: save. save. save.
another way to gain a lot of gold, is to sell gems. You may have done a lot of heroics and get the Stone Keeper Shards. You can use those, switch them to honor at Wintergrasp, use that honor to buy gems (i am not sure where the horde one is) in Stormwind. and sell those gems for an good income.
if you are REALLY REALLY risky, you can buy gold. but remember. do not do it to much. do small amounts spread out. and get an authenticator for small money, so you wont get hacked.
Even at this pace, it can take a LOOOONG time, not something you can do very fast.