Any suggestions that don't involve spending £1099.00 for a new G5 iMac?
There is no such thing as a new G5 iMac. They were discontinued in 2006.
The G5 is a reference to a PowerPC chip. Current iMacs use Intel chips.
You need to run Software Update on your 10.6.3 volume to get it up to 10.6.8. Then you will be able to use the latest version of iTunes.
iTunes 11.02 requirements: