I think the best and safest light set-up for the money right now is the MS900 from Geoman (c. $90 US) and DiNotte tail light (c. $89 right now + AA batteries and charger). That being said, Geoman has been saying a new MS tail light is imminent. There's really no detail available about it yet, so I don't know if it'll be a better value than the DiNotte.

I have said before, most riders seem to ignore their rear lighting. I think a highly visible rear light is more important than a good front light. If you can only afford one light, get the best tail light you can afford. Strap a flashlight on for a headlight if you have to. Among cheap/lights I already had, I've used my Minimag AA LED, Makita 9.6V, Task Force 150L. They all were adequate for low-ish speed road riding.