in QLD rego on a single seat bike is way cheap, so if just commuting for yourself look into that as a option in buying a bike.
in your bike choice- looks like you want your cake and eat it as well.
justify that you need another vehicle, as it will be cheaper- that only works on a cheap 250cc, but then that won't be any fun up around Tambourine etc on the weekends
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seriously seems like more of a life style thing, you still have the option if wet to use the car.....
oh and I admit that I have 2 cars and a bike for when the mood takes me
Single seat Ducati, costs around $1000/ year in rego, insurance and misc maintanance (oils filters) to sit in the shed + ~$500 in fuel, might do around 5,000km/s year so every second year tyres and service (of approx $1600) not every bike costs as much to run and maintain