From the websites I've seen, it's not a massive difference.
Here's two:
USA http://www.rocky-road.com/arb-air-lo...mpressors.html
Straya http://shop.snakeracing.com.au/searc...ery=Air+Locker
Using an IFS 100 series as a guide, on those two sites there's about $100 in the difference(take exchange rate into account).
Now this is just a guess, but I'd say they buy a sh1teload more lockers in the US than they do in Australia and probably also have more locally grown competition over there too, so they have to offer a lower price. Kind of makes sense in that context.
The tour was a definite eye opener for me, disspelled a lot of myths.