I got a HID headlamp and a 4500 mAH NiMH rechargable bottle battery with charger from batteryspace for about $170. I had to fashion a bracket (bent piece of aluminum) and wire it up. I put in a switch but you could get by with just plugging the battery in.

Just bringing it up; if you're already looking at spending > $150 for a halogen, HID is a great step up. Runtime is great on this too.