So, I haven’t tried this myself but it doesn’t sound too bad.
I had guildmates saying they would create a deathknight, go through the outland quests, send the money to their main, then delete the DK. Rinse and repeat. This works since outland quests give a decent amount of gold. It’s easy, chill, and it works. (Plus if you don’t have DK already, it also gets you an alt.) After one DK alt, probably not worth keeping the others. Don’t forget to send the money to your main before you actually delete the DK
Other than that, most profs can make you decent gold. Mining in outland, and later in Northrend, isn’t bad either.
Basically outland quests if you want a straightforward way to earn some gold. You could do profs and sell the mats, or attempt to sell what you create from those matts. They don’t always sell though. Prices are deflated right now, at least on the fresh servers, and your mats will be worth more down the line. If you haven’t finished all the outland quests on your main, feel free to grind them out while you wait for AV to pop or get a dungeon group.
If you happen to use RestedXP, there is a setting that takes gold into account. Meaning it will direct you through quests with gold in mind and not just leveling. For the DKs, you could turn this setting on when you enter Outland. Just enable it in the addon settings. Type /rxp to get to settings. I’ve never tried this, but might give it a go myself just to see how well it works.
A few profs are in need, like Inscription and you can make a decent amount on that right now. The prices are inflated since it recently became available in pre-patch. Making glyphs can earn you decent coin on the AH, but the AH isn’t for everyone. Other than that, at least on fresh servers, mats are pretty cheap. So they’re not exactly worth gathering, and I had ended up selling them to vendors because it was more profitable to do so. That wasn’t always the case though, especially in higher level zones.
You could always try and create in-demand gear for those not going with Honor gear but are new or on a fresh character and want decent gear. Most people seem to be doing the AV grind for honor, though.
In the end, questing in outland seems the most straightforward. You’re not risking anything either. I haven’t tried this method with making DK after DK, but I do know outland quests have good payouts. So, in theory, it seems like it’d work just fine.
Are you on a fresh server? The economy is different between the fresh and existing servers, so it’s hard to point you towards the AH or mat grind when I don’t know the current state of the economy on your server. But that’s another reason AH isn’t user friendly. If you can make some pre-raid BiS gear, people may buy that. Selling the equipment you don’t use, while it seems obvious, I still see some players carrying a bunch of stuff in bags that they’ll never use.
Now is a good time to clean your bank and inv. Wrath will replace a lot of the sought after mats, gear, and so on. Or, use those mats to level some profs to be ready for wrath, and make your money when wrath launches instead of having it before it launches. Lots of mats to farm in Northrend, and you’ll be there anyway.
I’d still say the DK method seems like your best bet. Especially with RestedXP and/or if you know the quests well enough to get them done quickly.