*broken record* Cateye volt 300 or Smart 700 both hit the OP price point and requirements. I've used both in complete darkness to see by and been totally happy doing so, the 700 particularly, it kicks out more than enough light to see by, both are USB charge (volt micro, 700 mini) so will sit and charge happily from a phone or camera lead plugged into a socket or computer, good battery life for both, very robust and reliable lights, multiple power settings for longer life as a backup, the volt does the dual steady/flash thing which I like and both are lightweight compact units that are easily pocketable.
I use either now in preference to my Chinese magicshine clone which while being waaaaaayyyyyy brighter (and far brighter than I'd need for anything other than the Glentress black run at 3am in December) needs a lumpy battery pack, isn't nearly as strongly mounted and gets painfully hot to touch.