Are there any old world herbs/ore in demand that I could farm for gold?
If you are keen on farming, and not playing the auction house there are multiple methods with minimum time investment that you can make gold. I've successfully used all of these methods a few times each and can give you more details if you want to PM me. Prices dependent on server.
Selling profession Kits:
Engineering 1-600 kit - 5-6 hours of Mining/cloth gathering, 6-12k profit. (Requires Mining)
Tailoring 1-600 kit- 8-10 hours of Cloth Gathering, 6-15k profit. (Requires a Tailor, and gear speeds up the process.)
Leather Working 1-600 kit- 4-6 hours of Leather Farming 6-12k profit (Requires skinning, and gear speeds up the process.)
Potion of Treasure Finding Farming:
Best classes for this are Destruction Warlock and Boomkin, other classes/specs can work but are much less efficient. Requires Tailoring, and possibly another profession for maximizing profit. 1 hour of farming can net 4-12k gold depending on your server. Minimum gear requirement for efficiency is probably about 522, but anything 550 or higher is preferred.
Leather Working Minimal Effort:
If you have the leather working profession and use the Halfhill Farm in MoP you can make leg kits for players that can sell upwards of 500g a piece. I have 2 leather workers and make 800-1200g a day for about 10 minutes of effort. 5600-8400g a week for a little over an hour of total work.
I've used all of the above methods to get all of my 90's geared (to many), their professions leveled, and a decent sized pile of gold for when WoD hits so I won't have to worry about sustaining my characters. With maybe 30 hours of total farming. Again if you are curious about the details of any of the above methods or have any questions feel free to PM me.