What size nest egg?

Randomly wandering through my thoughts for the afternoon, an idea popped into my head. More of a rhetorical question, but food for thought, nonetheless.

How much gold will be "a lot" of gold when Wrath of the Lich King comes out?

Blizzard engineered The Burning Crusade economy to make the gold earning capacity of those who purchase the xpac to be substantially higher than those who don't have the pack, as incentive to purchase the new software. They basically obsoleted the economy of the old world. Sure, you can make money without the expansion. H3ll, some people can make a fortune doing nothing but playing the AH with a low level toon starting with little or no seed money. But for the normal player, who is playing via questing, grinding, professions, and basic AH activity, its no contest. Outlands econonmy trumps Azeroth.

I'm assuming that pattern will be repeated going into the next expansion. The question on my mind is how much?

One way to try to predict is looking at the most tangible money sink in the game: epic riding.

To make the math easy, lets pretend that the epic riding skill plus a mount costs 1000 gold for epic galloping, and 5000 gold for epic flying.

Using just this as the basis for the whole economy (which is not really correct, but whatever, work with me here), Blizz made the expansion's major money sink grow 500% from original game into first expansion pack.

I'm not sure what the story is with flight and mounts and such in WotLK, but I hear tell that there won't be a new level of riding training as the next big money sink. Who cares, because whether its riding or not, there will still be some kind of single giant expense built into the game to help keep inflation under control. Or they might F things up entirely and build in a small-ish recurring expense on top of the already recurring raid expenses, but that wouldn't fit with my little thought exercise here, so skip that.

So how much will it be? They could continue in a linear fashion and increase the cost by another 500% over the original Azeroth prices, which would indicate that the next big boy will cost about 10k gold. Or they could continue exponentially and increase the cost by 500% over the Outlands prices, at a whopping 25k gold.

Naturally, which ever price they go with will be arbitrary, as the whole economy and game will scale equally, meaning that if the exponential growth option were chosen, that 25K gold would be roughly equivalent in difficulty to save as is 5k in the current economy.

What do you think? If one was to set a goal for a nest egg to carry into the next expansion pack, what would you go with?