The stands in the mall always have good deals on cheap glasses and also TJ Max. Thats usually where I get mine b/c I always lose them or my kids break them.
i second the suggestions for the sunglass stands in the mall. they always have a ton of styles (that are based off of popular brands, like ray ban) and usually have really good deals like 3 for $20 (or a price similar to that)
another place to go is target. some of my favorite pairs came from there, and they are cheap enough that i'm not too heart broken when they brake or get lost.
Forever 21 and H&M.
Except during the fall / winter season's they happen to get rid off them all to make room for the scarves and mitts ! But depending on where you are, I live in Canada so right abouts now were in the winter season.
Anyways happy shopping !
I got some at Nordstrom for $10 and they have lasted me 2 years so far. Go to the juniors section there and they have quite a nice (and inexpensive) selection!