Using a bike as a power source is nothing new, but the idea of providing your own power is getting more and more attractive as people find their lives full of energy-sucking devices. Nokia just a couple weeks ago started pushing a little phone charger for bikes, and if I ever bought another Nokia phone (unlikely) I’d definitely pick one of those up as well.
If you felt like building your own, though, there are also established recipes. This new one corrects a heat inefficiency in an older design by substituting a stepper motor, which is something I know nothing about.
There’s a lot of elementary electric engineering going on here (yes, and soldering), but other than knowing your polarities and such, I think this is a pretty straightforward project — as long as you can find a surplus stepper motor, and they don’t seem that rare. Total cost… I’m going to just ballpark at around $40-50 if you don’t have materials on-hand.
The only issue is that it provides just 5W, so the more power-hungry devices won’t get much of a charge out of that. Eh, what are you gonna do.