I remember a time in the late 90's when GT40's were not so widely known or available here in Oz, original cars were many hundreds of thousands of dollars, a replica monocoque from NZ was selling in 1994 for $300k, an imported GTD would cost about 40K GBP or about $120KAUS (3 to 1 back then) imported into Aus. An ERA was about $85kUS complete and imported to Aus making it about $170KAUS due to the 2 to 1 currency exchange rate back then.
In this environment, DRB and RF came into being offering cars that were substantially less than this, $100 -$120K on road and complianced to Australian design rules, which the others were not.
In the subsequent years, many other manufacturers both existing and new came out and found ways of challenging these companies in both price and specification and then, most importantly the exchange rate started to change making US - UK - SA cars much more affordable and Aussie built cars much less so. The cars you see on sale are the products of those times and reflect what owners have paid and therefore they are setting the value of these cars. It is a costly enterprise to achieve Australian compliance on these vehicles and one that I doubt international manufacturers would be willing to pay to achieve. If I was to sell my car overseas I know that it would be worth almost half of what they go for here. It would be possible for someone in Australia to order an RCR or a Tornado/MDA/CAV and then modify it to meet all the regulations here however it would be a pioneering road and the final costs would still be a bit of a mystery.
This is just my opinion of why we see such a difference in pricing b/w cars sold in Oz compared with prices in the USA and UK, I'm sure others can come up with a better explanation.
As an aside, is Australia the only place where GT40's need to comply to modern emissions and design rules?
Cheers
Bill.