$10 batteries
$ 9 Charger
http://www.dealextreme.com/details.dx/sku.6145
$17 flashlight

$36 total...add a mounting system and total for about $40 you would have an adequate lighting system for the occasional ride home at an easy pace and 1 or 2 hour ride.

While the light originally posted by N4 was overkill, it is a very nice light.