The light itself is fine. I guess the difference is, as slvoid says, quality of connectors and possibly mounting system. If you feel getting a bit better connectors is worth the extra money to you, go for it.
Personally I am not made of money so I got a bare fixture from them for $110 and wired it to my existing 12V system, so I have HID for pretty cheap. It has yet to cause me any trouble whatsoever after one full winter's riding.

I like a spot personally, but I haven't tried the flood, and it's bright enough that even a flood would probably light pretty far down the road. My spot has enough side scatter that I can still see fine close to the wheel.

But I suppose that in the future the connectors might crap out. If they do, it'll cost me about $3 and about 30 minutes to replace them since I used just standard rubber trailer connectors. Since those connectors seem to last years hanging down in the salt spray of a trailer hitch, I'm not holding my breath for them to die.

I was about to say that someone would soon come up with a cheap HID bundle suited for retail, but I don't think there's a ready market. LBSs are too wrapped up into selling high end stuff at a premium. Also the market is too segmented; they have weekend warriors buying high end stuff to ride 40 miles a week, then the unwashed masses who wouldn't buy an HID system even if it cost $50; they're going to go to Wal*Mart, and ride without lights. The only people looking for cheap HID are a VERY FEW (in comparison) commuters who are looking for functional stuff.