In the past, I've just dug my heels in. I always ask before I have whatever the scan or test is, and if I'm told they won't bulkbill and the gap will be $ whatever, I've simply said, "Well sorry, I simply can't afford that. I'll either not be able to pay my rent, or buy food for the next month, or I'll have to go and purchase a pair of black fishnet stockings and find me a streetlight every night for the next week". I've never had to pay extra...the receptionist has always either spoken to their supervisor, or has made a call and then told me that they will bulk bill me.