Not only have I been asked in game but I have seen a few blogs tackling the same topic. The common question I see is, “how much money do you think I need for the expansion?”
As an Enchanter/Engineering profession I found it very difficult to earn gold pre-BC. The only thing I really could do is sell any junk I had while grinding out zones where I had yet to quest. Raiding provided only a nice repair bill and rarely any type of profit.
Before BC was released my self-goal was to try to hit 1000 in gold. This was a huge challenge but somehow I managed. When BC was finally released, Blizz put our pocketbook fears to rest by increasing the money given by quests. This was a nice surprise for everyone.
Fast forward a few months and Blizz gives us a new way to make money by doing daily quests called Dailies (never would have guessed that). At first there were only a few daily quests out there and you were only allowed to do a max of 10 per day. Now we have over 30+ daily quests to choose from and we are allowed to do 25 dailies per day. So now anyone has the means to make good money, even if your profession doesn’t allow for it.
So what is a good amount to go for when the new expansion is released? This is my thought, so take what you will. Advice is free. ^^
The most expensive thing to come with Burning Crusades was the 5000g skill needed for your epic flying mount. So, in my opinion if you can save between 3000g to 5000g before WotLK is released, I think you will be at a very good starting point. Though it may seem steep, if you stick with your dailies it is completely possible. Whether you decided to reach that amount collectively through all your toons or for each individual toon is your choice.
This way if you have a nice head start in saving, the cost of skills, respecs, professions or hefty repair bills won’t catch you off guard.