You'd be surprised how far a G3 iBook can still take you.
Being a junior in college right now I'm running 10.3.9 on a 600Mhz G3 iBook that I picked up for $350 about 2 years ago.
Contrary to what you might expect, I can write essays, listen to iTunes, chat, and waste time on the 'net just fine.
Consider what you're going to be using it for. if it's going to be your primary, be prepared to make do with just the bare minimum. If you just want to use it for the very basics while you use another computer for your entertainment, I couldn't think of a better idea at a better price.
My battery is 6 years old and I still get 3 hours of charge out of it consistently with full brightness and highest processor speed setting.