I would try wetsanding the scratches out before dropping money on a new housing. If the scratches are deep start with 180 grit and progressively work your way up to 2000 grit then polish the wetsanding marks out with either a headlight restoration kit or a DA polisher (porter 7424, etc). Both the restoration kits and wetsanding sandpaper packs can be had at local auto parts stores or even walmart. You'll probably have ~$25 dollars in supplies to try the wetsanding approach vs. $100+ for a new housing.
Here are the two Depo branded Mach HID replacements on Amazon for ~$130 each:
If you do get a new housing I would be very interested in buying the weather stripping off your old housing if its still in decent condition.