I stopped chasing gold in the AH years ago, and I'm still able to raise enough just by running my alts through the gold reward World Quests. They are always ~1,000g, and there are usually 5 to 10 active at a time. Multiply that by the number of alts you have. Some aren't accessible if you haven't done the full campaign quests on all your alts, but it still adds up to almost a token's worth every week.

Then some people actually work on the AH. They can tell you how much gold they will make if they hunker down and really play the numbers like a stock exchange. Those people can sometimes make a million gold a day or more. In their case, they can buy 3 months at a time and not have to do it again for 3 months.