Well, Cataclysm gives around 10,000 Gold and the same with WOTLK (though it depends how many zones you've already completed)
- The lower end ones (1-60) doesnt give all that much... around 2g at max for a quest around level 50-60
Doing Loremaster, Explorer & some of the easy WLK meta achievements gets close to 10,000 achievement points (got 7.1k on my new main) and not even finished 10% of loremaster yet.
I'd say definitely try to do loremaster before MoP comes out, with the changes they are making to not let you pick the gear from the quest reward it'll lower the amount you make off of questing (since you won't be able to pick the highest gold value item to vendor). It's a small thing but it adds up.
Also depending on what class you play and how geared you are you can look at soloing some older raids for gold and achievements.
when i leveled from 80-83, i got around 5k. so i would say all in all, 15-16k. might just have been lucky with greenies that i sold. also, picked the things i could vendor for the most gold if i couldnt use an item that i got as reward from a quest
I cannot say anything to how much gold you will make but some other points...
You might better get enchanting since I quess dusts and essences propably get you richer than vendoring greens.
Also you should be spending gold before mop because when mop hits, there will be much money pumped to economy from leveling quests and new dailies-->quest rewards-->inflation