As a general rule the prices will go down the closer you get to the fest. I saw a thread where a guy graphed the average price of stubhub tickets for Coachella. It was a steady decline from almost $600 to just below face value the days before the festival.
The reasoning behind that is there are less and less people who can get 5 days free the closer you get to the fest. The sooner the better for selling it I'd say.