G3 ibook battery replacement advice?

what's a good source for replacement batteries for a G3 500 iBook? A new one would cost $129 and that seems like too much to pay considering the current value of the old ibook plus the fact that I'll probably replace it sometime in the next 6 to 12 months

anybody have any luck with used batteries bought off of ebay? any other ideas?

I'm only getting 20 to 30 min out of my current battery which is really not enough to be practical. If I could get a couple of hours out of a used battery then that would work ok for me. Cant see spending all the cash necessary for a new battery though since I only use the ibook occassionally for travel, especially since its only worth a few hundred dollars anyway