There have been a couple of threads talking about LO's losing glasses. My suggestion has been to stock up on them because they are cheap and not worry about it. Goggles4u is having another one of their frequent sales. Right now it's 2 pairs for $10. There's also probably shipping which is like $5-$7 if I remember right. Sometimes they ship for free. Now this isn't a big save since the regular price is $7 for a pair so $14 for 2 pairs, but $4 is $4. This is for their cheapest tier of frames and the cheapest lenses. They work fine though. I'm wearing a pair of $5 specials right now. They look like they cost much more than $5.
The website is goggles4u.com and the coupon is "2FOR10".