That's a G5 PowerPC based iMac not Intel based. Won't run anything current. Stay away.
Cheers,
That's a fair price, but that model has issues with power supplies and bulging caps on the logic board.
I don't know. In the US I don't know too many people will to pay $500+ for a G5 iMac. Perhaps prices are significantly higher in the UK. Regardless, its a pretty old machine. I wouldn't pay anything for such a machine.
Cheers,