I've completed a darkmoon deck today, and I've tried to sell it before the price drop. I've shouted in /2 and one person whispered me, offering to buy my crane deck for 24k. I have sold it and in two minutes another person whispered me offering my 25k. Apparently, I have already sold my deck, but then I've got this idea. I have checked the AH prices for decks from ace to eight and found out, that I could create a complete deck for under 18k if I'd buy it off from AH.
I have sold another seven complete decks today, each netting me at least 4k gold.
OF COURSE IT DEPENDS ON YOUR SERVER.
tl;dr version:
1. Advertise Darkmoon decks on /2
2. When you've got your buyer, buy out single cards from AH. They are sometimes cheaper than for what you'd sell your deck.
3. Profit
If you want to do it, do it ASAP, because I think the prices will drop when the DMF comes.