Zenni Optical - Buy 2 pairs of glasses get 1 pair FREE! - From $6.95 per pair!!! (ends 14 Mar)
Basically, buy 3 pairs of glasses and check them through.
The cheapest one is free!
Not sure when the offer expires, as it is not stated.
However it says for a short time only.. so be quick!
I have been a repeat customer of theirs for years. Their cheapest glasses (complete set) start from $6.95!!! Shipping to Australia is a flat rate of $9.95