Simple answer: if you don't want to fork over the cash to do it right, then dont bother.
Long answer: Ebay projectors, not the headlights, but the actual projecter element themselves are not very high quality. They produce uneven beams of light, and as a result, produce less usable light than the stock reflector headlights. Putting HIDs in these housings does not improve this as the housings are not designed to withstand the heat that HID bulbs produce. Before long, the reflective surface inside of the projector burns and bubbles, which reduces light output even more, and causes even worse patterns in the beam throw. Either way, you end up with less light than a OEM headlamp.
By retrofitting these headlights, i am effectively removing all of the actual light-emanating components and replacing them with equipment designed to handle HIDs.
This is a matter of some debate on the forums, and the rules are not to argue over it, so i wont say anything about what i think of people who take the cheap route. But, i will say this:
Putting HIDs in (reflector OR projector) housings that are not SPECIFICALLY designed for them is Illegal, Dangerous to oncoming drivers, and does not (no matter how you want to argue it) produce more usable light than halogen reflector OEM housings.
So, either fork over the cash for a proper HID setup, or stick OEM.