HID question (one side burnt out)

[stateofidleness]

Got these a while back after I just got the car, so may be 2years ago. Tonight I noticed my passenger side HID bulb was not on. I have them in my low beams and usually use them as DRL's as well.

I'm gonna do some swapping of stuff tomorrow to see if it's bulb or ballast, but what's the usual cause here? bulb or ballast?

the kit I bought was a pretty expensive set from Vivid Racing, but I don't see them on the site any more.

What other kits have people gone with and had good luck?

[stateofidleness]

so much feedback!

ended up getting a 'cheapo' replacement kit.. cheaper than a single replacement bulb!

came out to $69 shipped for anyone in the market (no affiliation) http://www.hidsrus.com/porsche-boxster-xenon-kits-lights-conversions-headlights-bulbs/

2 year warranty, so i figure if it dies on me, it's under warranty and/or it'll be cheap enough to get another one.