Craig
You definitely want to shop around before you buy, even if you've decided you want a 12" dob because there are considerable variations in pricing. I'd recommend checking out:
www.bintelshop.com.au
and
http://www.andrewscom.com.au/
Make sure you inquire about shipping costs because that can also vary dramatically.
As others have said, a 12" solid tube dob is a BIG scope, if you plan to transport it make sure it will fit in your vehicle.
regards
Stephen