This US firm is one of the best out there for cheap prescription glasses/sunglasses.
Their Fourth of July sale is the best you'll get.
Non-sale base offer is US $39.00 + US $12.95 shipping (= US $51.95 ~ AU $71.00), but with US $20.00 off takes it down to around AU $43.50 (cheapest frame, clear).
You'll need to pay a little more for tinting (sunglasses) and better frames.
They also have a 20% off total order going (not stackable).
I would go black plastic frame for reading/sunnies/backup - you may wish to avoid metal frames as they require a finer touch when grinding the lens down. Also be careful with sizing - some are made for midgets.
Can you claim this from priv health fund?