Check your local Wal-mart and see if they have any Mag-Lite 2 AA 3-watt LED flashlights left. They've been on clearance sale for $19 in my area. That 3-watts is not the rating of the LED! It's compared to a standard flashlight with a 3-watt filament bulb. It is a nice light for the price however and worth the money. It has an adjustable beam pattern making it a very good all purpose light. It will run for 2.5 hours on standard AA alkaline batteries. I mounted my Mag-Lite to the handlebar using 1/2-inch EMT conduit hangers.
Be sure to glue some bits of old inner tube rubber to the interior parts of the conduit clamp to promote a form grip and prevent scratching your flashlight.
I also drilled a small hole in the battery cap and used a section of old fiberglass tent pole to make an external battery pack adaptor as can be seen in the photo below.
2 D size batteries will last much longer than 2 AA batteries!