Worth broken is dependable on the condtion of the powerbook and the specification. Those places that say they will pay out for used old laptops and phones, never pay what they value them at. Sadly there is no way of upgrading a Powerbook to match that of a MacBook. The only items your can upgrade are the memory, hard drive and OS.
Fixing it really does depend, it could be as simple as the DC inboard or power adapter needs replacement, or a terrible as a complete logic board replacement. A logic board can be replaced but at great expense.
You really need to run some diagnostics on the laptop. A shop could help you with that.
Best of luck