H.I.D. Xenon headlights. questions help please.
 

Ok so my question about the hid's on my 06 cooper s. Last week the low beam on the drivers side went out. I went to oreilys and the guy said $90 a bulb. Ive seen pairs of the xenon bulbs on ebay for as low as $25. First are these of inferior quality or something? Secondly ive heard they are hard to replace.
Other than that ive noticed the light will flicker at first but not turn on is it possible that the hid/xenon ballast is bad? How would i know for sure? Thanks for any help.