Thanks to all for the useful info. With that feedback and emails to CASA Canberra, this is my understanding:
CV: Easier than SPECPL because AVID or ASIC are not essential. So if you are careful where you go that would be $260 for 3 months. I had one in 2005 (and got an ARN issued then) but you have to do the whole thing again, less the UK CAA verification part. BUT CASA need certified copies of logbook,licence and medical all over again. Certification of the copy docs is the problem as I think that needs Oz officials. So I think its better to go to the local CASA, have them do it free and they post all the stuff to Canberra. Pray the latter process it quickly
SPECPL: Almost identical process for the licence and same fees, but valid 2 years. BUT because this is a licence (CV is not) then photo ID (AVID) as a minimum needed. If going to main airfields, need an ASIC instead.
Main problem for foreign pilot is authentication of personal documents which can really only be done in Oz by certain classes of persons. Police checks both in Oz and in home country will take time, and in the UK will cost. So better deal for multiple visits but a hassle to start off?