The price would gradually reset by itself back down towards 4 wow gold.
Considering the stakes of my bet, I decided to take a gamble. I took every copper I made in that final Darkmoon Faire and began buying up Whiptail and Twilight Jasmine I could find. I turned my bad druid alt into an ink factory, using the Panda addon to mill hundreds of stacks of herbs a night. When I headed off to the gym, I'd leave my computer running, AFK creating hundreds of inks in my absence.
I was limited only through the speed at which farmers could pull the herbs from the ground. Some nights I bought, quite literally, tens of thousands of herbs. On other nights, I didn't buy any. Some nights i experienced been lucky sufficient to find somebody in promoting his freshly picked lot, and if i experienced been particularly lucky, they'd be ready to sell me even more the next day.
I was always careful, though, to set a price ceiling; a price which I would by no means pay more than. If I logged on to find Whiptail promoting at 4 wow gold a piece, I'd buy as many stacks as I could find up to, say, the 6 wow gold a item line. As I milled over the next day or two, the price would gradually reset by itself back down towards 4 wow gold. My presence in the market pushed the price of herbs up by 20 or 25%, and that's only because I wasn't ready to force the costs even higher.