Check out the forum: HID Planet. They have a great source of information regarding retrofits and what to avoid. And to your question on anything premade, yes... 'almost' all e-Bay items are garbage and should be avoided. You will be putting yourself and others at risk if running them due to their poor output. If you do not want to save money to build yourself a retrofit, there are plenty of companies and people out there who do it often enough to provide a very good option. I have been running a plug n play kit on my factory housings and hate the fact that I'm blinding people every time i'm on the road. My output is scattered and have no focus to the beam. I am currently having someone near by me build me a true retrofit. I am using the RX-350 bi-xenon projectors and will be running a 4200K bulb for maximum lumens. ANY bulb that is above 6000K is garbage and you will be sacrificing light output. You can get a great white light with some blue tinting with a 5000K or 5500K set and still utilize the most of the lumens and output of the bulbs.
I hope this helps, and best of luck...
Joe