I good set of HID generally will set you back around $300. Of course you can piece together name brand parts and make yourself a used one a bit cheaper.
I have the $100 China HID lights in my truck. The worked great for about a year, then one started to flicker, and finally that one wouldn't turn on. I bought the"upgraded" harness which wires them directly to the battery about 2 months back, and they've been workin well since. If I run into another problem the halogens will be going back in.
-Cyrus