How about the cost of at least two visits by an approved person flown up from Australia, firstly to inspect the aircraft, and the second time, to issue the certificate.
A cheaper option would be to use someone already in Europe, who has the necessary Instruments of Appointment to issue CASA CofAs. Try here:
Paper Planes
Edit: Although I guess maybe not if the aircraft won't have a CofA. I'd still contact Michael at Paper Planes for some advice.