The main way I save money on glasses is to decline fancy lens options and then pick from the cheapest price bracket available on frames, usually I can find something from the 'clearance' section.
I have bought lotsa glasses over the years and am totally unconvinced that (for basic plain-vanilla type glasses, anyhow) there is any meaningful difference in *quality* among chains. Everywhere I've ever tried has been willing to redo a lens if it came out too different from prescription; and every time I've ever in with a broken pair, stores have been happy to repair it if possible (sometimes they've even done it for free *without* it having been *that* store that I bought the pair from).
If you want more than one pair (e.g. if you need prescription sunglasses) it is heavily worth waiting for an appropriate sale, too.
Good luck, have fun,
Pat