Buy the 80+50 stacks, leave the 100, and come back the next day to nab more from people who undercut the 100 because they couldn't afford to buy it out.
Ban wave on Bots, Pirox getting shut down, 4.3 release which led to people needing tons of gems, which led to people seeing an opportunity to control the market. It's a mix of different things.
Should start to see a slow decline in the price of ore soon, Now that everything has settled a bit with the new 5 mans and DS. With LFR there are a lot more people running DS and a lot more geared out alts.