Not many LED systems I know of produce enough light to actually see the road. Those that do are very expensive. I think they will be the way to go (low power consumption, durable bulbs, compact design and lightweight) in the future but not yet. Still, you could try some of the more affordable models, such as the Cateye mentioned above, to see if the amount of light they put out is enough for you. If it is - look no further.

A good hub dynamo (=SON) has very low drag when the light is switched off, and high efficiency when the light is on. It is also immune to bad weather and snow. A bottle dynamo has obviously no drag when switched off, and the best of these (Lightspin, Busch & Mueller Dymotec S6) compete with hub dynamos in terms of efficiency. They do not cope as well in snowy or muddy conditions. A self-powered light would make sense in many ways when touring. Downside is, a SON or both bottle dynamos mentioned are way over your price bracket and you would still need a backup light for roadside repairs.

Probably cheapest lights for actually seeing the road are still halogen based. There are helmet mounts, if you wish to put the light on your head. You can also do one yourself, see the (in)famous Total Geekiness thread in Commuting. I have a modified Vistalite 10W 6V system, but it would still require more tinkering (lighter battery and longer burn time) before I would agree to haul it with me when touring.

--J