2001 Cadillac STS HID Headlight System -Ballast Replacement

2001 Cadillac Seville STS - My passenger side low beam headlight recently quit working. I thought that I could just replace a bulb, but it turns out that it has the OEM HID system. Once I realized this I tried swapping the "good" lamp from the drivers side but it still doesn't work so I assume the the problem is with the ballast.

I have two questions:

1. Where are the HID ballasts located on this car and how do I get to them in order to replace them?

2. Is there a less expensive ballast replacement option for this vehicle? On-line GM parts sites list the replacement ballast at ~$600 and sell it for ~$430 each. After market ballasts can typically be purchased for $40-$80 each. The GM parts sites also indicate that the original ballast is no longer available and that an adapter cable cable will be required for an additional $30 to make the replacement ballast work. This suggests to me that the replacement ballast is a standard ballast that could be purchased for significanly less $ if I just knew what to buy!

I have already located two new D1S lamps for $45 for the pair (GM wants ~$300 each!) And I would go ahead and replace both ballasts and both lamps if I could figure out where to buy the ballasts for a reasonable price.

I have searched the internet for a couple of days and not been able to find the answers to these questions! So, your help with this would be gratly appreciated.

Thanks,
Dave.