CLR Calcium Lime Rust Remover 750mL $9 @ Officeworks
750ml on clearance at Officeworks for $9 - in store and online.
Normally $16.10 at Officeworks, can be had for $13.40 for 750ml at Woolworths or $18.40 for 1L at Bunnings.
Have used this to good effect on older baths and bathrooms for removing rust, grime, etc. and cleaning up around taps. Good for a bunch of other stuff too one would assume.