Well, you will have to pay fees, taxes and shipping, which is just the start. Aircooled VWs are also worth considerably more in the UK, so if you wanted value for money you'd be better off selling up over there and buying another Beetle here where they're cheap. There aren't many convertibles around here though, so if you wanted one then it might be a bit of a search.
The big deal with importing used cars to Australia at the moment is that it has to be completely 100% stock standard. Modified vehicles are not allowed in, and there are rumours suggesting that cars have been knocked back at the docks for modifications as trivial as different wheels or even paint. Once it's in, LHD cars are not allowed to be registered with any modifications anyway, so it would have to be either kept in original condition or converted to RHD. Check out some information here:
http://www.infrastructure.gov.au/roads/vehicle_regulation/bulletin/importing_vehicles/index.aspx
The reason for all of the hassle about modified cars is due to a recent change in the government's interpretation of the law. The basic idea is that a car may only be individually imported if it was made before 1989. However, the catch is that if a car is "converted" then the date of manufacture is considered to be the date at which the modifications were completed, not the date listed on the car's title. This essentially was used to prevent things like hot-rods and kit cars from being registered as old vehicles when they are in fact new. It used to be that you could get modified production cars in. Depending on who you believe though, the people responsible for deciding what constitutes a modified car and what doesn't have recently started to ban anything which isn't a 100% restored or original car.
Below I've included a link to a 3.2MB pdf document showing a sample of some cars which have been refused for modifications and some which were approved for import. It's worth noting that all of the examples of approved cars given have their stock wheels and hubcaps on still. One of the rods which they refused is quite mild as well. The blue Model A 5-window has no engine showing, no body modifications at all and only the wheels, ride height and paint immediately give it away as a hot-rod. Presumably this indicates that if you change the wheels, paint and ride height of any other car it will also be refused entry to Australia.
http://www.infrastructure.gov.au/roads/vehicle_regulation/bulletin/importing_vehicles/general/files/examples_of_converted_vehicles_16July2010.pdf