Curious question... what is the difference between OEM phillips that are so expensive and chinese bulbs that are 20$ a pair. Clearly the oem ones will probably last longer but you can buy about 10 pairs for the price of 1 oem bulb!!
Why not just buy a pair of chinese bulbs?
Lots of people ask that Q. The Philips ones are high quality, they should last for a long time, we are talking usually 4 years+ easy. I am still running the OEM HID ballast and bulbs on my headlights, its a 2002, so 9 years now! One side is starting to flicker a tad from time to time, but its still working, and the colors are still OK.
Chinese bulbs are cheaper, and depending where you get them from, they actually can last on average from 1.5 to 3 years+. I have them on some cars so far for 2 years+ without issues. But you are right, for the best bang for the buck, the Chinese bulbs would be a better idea most of the time, and this is specially true if you consider the ballasts into account. Bulbs are cheap, ballasts are not.
Personally, for a relatively new car (say 2009+), I would get the good stuff like Philips because chances are you are going to keep the car for a while, and you dont want to switch HIDs every 2 years or 3. For older cars, I would get the Chinese ones and replace once if needed, it would be still cheaper, and you would probably sell or trade the car before they even go out.
If however you purchased the Philips ones, and for whatever reason they failed prematurely (bulbs/ballasts), or in case of an accident/hit and run/etc (god forbid), well then things will end up being very pricey at the end of the day.