Hello there.
My name is Bjorn and I'm one of the two at customlightz.
It's understandable why people get HID kits for $300 and call it a day, but if you really want to enjoy HIDs the way they were meant to be experienced there is only way: HID projectors.
Now for those who are curious, the price range for a retrofit varies a lot, and it mainly depends on the projector. You could get all the parts you need for about $350. This would include E46 projectors [the one in BMW and Benz] with bulbs and ballasts. You could also spend as much as $400+ for a pair of S2000 projectors.
I'm new to this forum, but I"ll try to come back and answer questions.