Thats a good price. I researched a MiniG4 for about a month looking for a home media computer. I eventually bought a 1.42 gHz 1gb/80gb BT/AP for $400 and I thought that that was a bit too much. If this machine has BT/AP on it then totally go for it.
I would suggest buying an Intel if you want any sort of longevity out of the machine. But if you just want a cheap machine for internet, you can't beat that price.