3d/Animation Software for Old iMac

My son has a 400 Mhz. G3 iMac with Panther (OS 10.3) on it. I'm looking for any 3D/animation software packages that might run on the machine (preferably low-cost as he is wanting to learn 3D/animation).

Anyone have ideas of what I might find that would run on it?

Thank you!

wncmacs