Gem Shuffling and most markets pertaining to raiding will be dead for now. It's best to simply farm up materials to sell, of all sorts.
I've been farming some 1-450 ores. most from outland > sells for 150g/stack on my server. Places are dead, so its kind of a gold mine atm.
Honestly, making 20k should take about a day or two if you are only using 1 bot. Your best bet is to farm ANYTHING. Yes, farm anything, it really doesn't matter. Because when MoP hits people will be rolling new toons & they will need to level professions. So whatever you are farming, someone will need it. Herbs, ore, fish, leather, cloth, pets - ANYTHING - people will need your stuff, lots of it, and all levels. This is how you make millions in the 1st few wks of an xpac.