While I cannot comment on the cards themselves (though their speed is rated at class 6), I can provide some input on minimising the shipping costs. You can take a look at some US shipping services (aka. priceusa, shipito, comgateway) and have the products shipped to their "warehouse" at us shipping rates (NB. try to find one that has an address in a 0% tax, such as Oregon) and from there you can have it shipped to Australia. Though since these are small items, you may want to do some consolidated packing to lessen the impact of the shipping costs.

The other question is whether the stores will accept an Australia Credit Card, etc.