I did the same in WoW :) Bought up all the versions of a certain item in AH and sold at extreme markup over time. As more came up on AH I’d just buy them all up and continue. This lasted for quite some time and I diversified into other items. Let’s just say I could afford anything in that game :)
In my case it was the egg needed for making a gingerbread cookie on Christmass. There was only one low level area that would drop them 100%. So I farmed it en-masse, no one else did.
