In World of Warcraft, you don't bank gold (money). Each character technically carries all the gold they have around with them. Open your backpack to see the amount of gold a character has (count should appear at the bottom of the backpack window). The only way to lose gold is by auctioning something on the AH (listing fee), bidding on something in AH, buying something from the AH, buying something from a vendor, repairing, trading to another character, sending gold away in the mail, or training. As long as you manage those things, you manage your gold.