alt Hacker NewsThe old-school dynamos cost 10-20 bucks: https://axabikesecurity.com/product/axa-8201-right/
They're just generic AC motors held against the rim, as simple and cheap as it gets. Nowadays I'd add a basic voltage regulation circuitry to get a stable 5V DC out of it.
That's why I said "reliable" in my post.
You'll spend more time futzing with one of or dealing with weather-related failures that you would have saved more time charging a pile of batteries before every ride.