I wouldn't go too cheap you're just asking for trouble and the lights are not very bright. Hub generators are the best way to go and Sanyo makes the lowest costing one at just $50 for the hub, then you have to add in the cost to have it built around your front wheel. Then Phillips Saferide 60 makes a great generator powered headlight at around $100.
Or you can contact Peter White Cycles and he can build you a generator hub front wheel and light plus tail light if needed in a package deal.