Since the mount changes coming in the next patch were announced earlier this week, players have had tons of questions about how the new mounts will be bought and used. I'm sure you know by now, if you've hit level 40, that buying the riding skill for mounts is 20g, normal mounts are 80g, and epic mounts are 900g. But in the next patch, there will be two levels of riding skills, a lower level (75 skill) for 90g, and a higher level (150 skill) for 900g (take a guess which kind of mount will probably require 300 skill...). Because the skills price will grow, the mount price itself will drop-- only 10g for each normal mount, and 100g for each epic mount. The overall price hasn't changed much, but the skill is much more expensive, while the mounts are cheaper.
First, of course, everyone wants to find out what happens to the mounts they have now. Hortus tells us, thank goodness, that if you have a mount now, you will have the appropriate skill to ride it when the patch hits. Paladins and Warlocks will get both their mounts and the required skill from their quests. If you have a PVP or AV mount, you will be given the 150 riding skill just like everyone else. All mounts will be BOP after the patch, so if you're holding a mount for someone else, pass it off soon. And finally, due to the new mount prices, I figured it would be lots easier to get lots of mounts. It will, with the faction, but to get other factions' mounts, says Hortus, you'll still need exalted with the other faction. So there's still a good amount of grinding in there if you have a horse and want a tiger (or an elekk...).
Finally, we here at WoW Insider know exactly what your real question is: "How can I do it the cheapest way possible?!" Things are still open to change (of course), but the cheapest way to get a mount and skill seems to be this: If you don't have the money (or level) for an epic mount, buy a skill now for only 20g, and when the patch hits, you'll be given 75 skill along with everyone else, and will be able to buy a normal mount for 10g, giving you a mount and skill for only 30g (normally 100g after the update). But if you have the money for an epic mount, buy one of those for 900g, and when the patch comes, you'll be given a riding skill of 150 (because you have a mount in your possession), and you'll already have the epic to go with it. In that scenario, you're only saving 100g, but as anyone saving for their first mount will tell you, 100g is plenty of money.
Update: A previous version of this post listed the wrong patch for the mounts. Thanks for the comments.