BuyDig offers the refurbished Jawbone UP Fitness Tracker in Black, model no. JBR52a, for $14.99 with free shipping. That's the best deal we've seen for it in any condition. (It's also at least $5 less than the lowest total in-stock price we could find for a new unit.) It's compatible with most Android and iOS devices. It's available in size S only.
No warranty information is provided.