Dynamo hubs have severe disadvantages? Like what, exactly? You can get ones that don't cost any more than normal road hubs, like this:

http://www.peterwhitecycles.com/sanyo.asp

With an inexpensive rim like a Sun CR-18, and straight 14ga spokes, I could build up a complete wheel for less than $100. A Lumotec Lyt that puts out 25lux is $50. If you're serious about night time riding, this is a good combination.

Now, I own a SON28, which was expensive. But I only had to buy it once, and I've had it for 6 years. I switch it out among my road bikes if I want to take a longer ride at night.