I don't buy the 30k gold when you hit 80 bit. 1-60 you will be negative 180g or so because with RAF you will level faster than you can loot to buy your spells. 60-70 questing you will only end up with about 800-900g per toon by the time you hit 70. Subtract spells, the cost to 60, and flying. You will be about broke even. That leaves 6k gold to earn per toon in 10 levels of Northrend. Not counting -5k gold for Northrend flying

Sure you can make a dime or two with tradeskills but not that much unless that is all you do instead of level to 80. There are just not enough rocks to find, berries to pick, animals to skin, or shinys to disenchant unless you dedicate a lot of time to just that.