Paypal website payments standard is your only option here. Unless you want to bill in AUD, you can't really use a merchant account in Australia. It's technically possible to use NAB to acquire in foreign currencies (ie. USD), but it's not feasible for small startups due to cost and complexity and the bank not actually knowing how. I lost my real HN account because I'm an idiot or whatever, but send questions to [email protected] if you want to hear about our various failed attempts at recurring cc billing.