hc, if you need your glasses every waking hour then you need a second pair anyway, in the event of a breakage/loss, surely? Why not post a cheap(ish) pair of frames to them? I sent a pair of Animal frames to them that I got from eBay for £10 and had them turned into prescription sunglasses for next to nothing (£19 I believe).
I've had Nike, Ray Ban and Oakley frames reglazed with them, never had a hitch and had the glasses back within 6 days.
If you don't like their quote they just send your frames back to you, free of charge.
Bar that, keep shopping around yourself, you won't get them much cheaper than the site I mentioned!