BitVice MPEG-2 encoder has a G3 version that can be had for only $56. It's just not optimized for G4s, but has about all the same features, and is apparently optimized for G3 chips(will still run on G4s though). The speed isn't half bad. especially for just doing AMVs. Sure beats $300+ for an encoder, or trying to transfer edit files over to a PC(or run on Virtual PC. Homer: Mmmmm, time-consuming...
Can't compare the quality of output to the more expensive encoders or the ones available on PCs, since I haven't really tried any before, but what I managed to get out of it looked great.

