I'm building a triple Seoul LED bike light, my LEDs just came in from Hong Kong, so gotta get going on that. I'm going to model it after this one but probably not using that style of housing. It should be almost as bright as an HID for a total cost of about $100 including the battery, $120 with a charger.
http://myfwyc.org/bikeled/DIY_LED_Bi...ing_Guide.html