It really depends on what is going on. My level 75 dks each have almost 2k each on them right now but that is only because I have nothing to spend gold on. At 80 I will start gearing one of them and get him an epic flyer they will probably go down to 40g each, enough to do repairs if needed.

If you are asking about loot in general I loot with the main and dump everything on the alts when his bags get full. Greens are sent to my enchanter to be DE'd, blues and other valuables are sent to a bank character to be stored or sold.

Other then training and mounts I never buy anything until I hit the level cap. All there really is worth buying is a couple epics for each class/build and your raid consumables even at 80.