Mostly what is available for a reasonable price is some small Japanese thing, with manual transmission. Also, inquire on how restrictive they're going to be on driving on gravel. On some major routes a gravel stretch is unavoidable. Or don't inquire and plan to wash the car before returning it. Gas is pricy, by US standards.
Gas is sold by the liter, of course.
Gas stations were the one merchant that I could usually count on to take my MasterCard. Drivers are generally courteous everywhere you go. The exception is in and around Sydney, where drivers are more aggressive and faster. Add to this the claustrophobic lane widths and it can feel positively harrowing to drive in or out of Sydney. Sometimes I felt very old.