Anytime the govt here needs to raise some money the first thing they do is increase rego and tolls. Our rego is over $600 pa including CTP and our car is 4 cyl. But we used to pay over $800 a year when we had a V8. Personalised plates cost over $400 to buy, but thankfully it is only a one off cost, no ongoing fee to have them (yet).
While I sympathise, personalised plates are a luxury - rego is a necessity so I don't think you can complain about how much they cost.