Ausspecs - one pair of glasses $35, two pairs $67.95. Includes lenses AND provider number!
*Update* You can currently get some pairs for $35 ('aviator' style, and a kids frame - links in thread below), although most standard vision frames & glasses are $38. The two pairs for $67.95 includes most (not all - just the ones that have a star next to them) from the $38 range.
Note - postage is a flat $8.50 (registered post) no matter how many glasses you order.