If you do it properly and get the washers and level sensors you are looking at over a grand. You would have to be mental to go down that route.
Either A: Get uprated bulbs (I have 5000k halogen bulbs which dont quite give the HID / xenon look but are a million times better than what was in there, cost a lot less and took 2 minutes to fit)
or B: Get a HID conversion kit. No idea on prices, take a butchers on Google -
http://www.hids4u.co.uk/The debate about the legality of these kits has been done to death, if you interested in them do a search, its all in there.