Intermittent Headlight Problem

The passenger side headlight of my fiances 2007 Prius keeps going out intermittently. It's a touring model with HID's. I replaced the bulb already and the problem persists. I searched and found that there is a TSB about it ( http://www.justanswer.com/uploads/johnduh/2008-11-27_191540_T-SB-0030-08.pdf ).

From reading that, it sounds like it's either the bulb (which I replaced), the wiring, or the HID ECU. Is it usually one or the other? Any idea on cost for the HID ECU?

 

Now it's happening to both sides. The drivers side went out today while the passenger side was on.