When these bulbs go, they really go. One blew on my a few weeks ago the the whole thing melted. Ebay is the cheapest place to go. Dealers here in Canada want $300 a bulb!!! Aftermarket places run from about $70 to $170. All for the same bulb.
When you order from ebay, just make sure you get the right colour. If I remember correctly, ours is 5000. They come is many colours 5000, 6000, 7000, etc.