Why answer if you don't even know and are just guessing?
The flying mounts themselves aren't that expensive. It's the riding skill that's expensive. There's also 2 types of flying mounts, a regular one and an epic one, just like the landbased mounts. Both require level 70 (though druids receive a flight form at level 68). The flying mount is required to reach certain content. The epic flying mount is not required at all. It's just a lot faster.
You need 225 riding skill for a flying mount, 300 riding skill for an epic flying mount.
Upgrading your riding skill from 150 to 225 costs 900g. Upgrading from 225 to 300 costs 5000g.
The flying mounts cost 100g. The epic versions cost 200g.
At the moment there are no special mounts for paladins and warlocks.
Edited, Dec 19th 2006 4:54pm by ThelsDeKwant