My boyfriend and I buy groceries together and it ends up costing us $100 a fortnight (roughly). That's only after you buy all the staples, like spices and flour and butter and tomato paste such. We eat fairly healthily, meat and vegetables and fruit and such, a lot of pasta and rice though, and a lot of cooking in bulk and freezing it to reheat later. There's a bulk supabarn store out near the airport which is slightly cheaper for most things. You definitely want to factor in more than $25 per week though, because you would still go out for dinner sometimes and sometimes things are more expensive than normal and sometimes you randomly feel like going out for ice-cream or baking some cupcakes.
I don't know the weekly rent off the top of my head, but it's that plus $25 for utilities plus whatever you spend on food. Plus $3 per load of washing (I tend to do washing once every 2-3 weeks, but I have a lot of clothes). Parking at UniLodge is also more expensive if you're bringing a car.