Wow, how funny to know I'm not the only one who experiences the "inverse law of sunglasses".
I have two pairs right now - cat-shaped tortoise shell ones from Target, and a 70s inspired pair with pink lenses and no frame from Limited (I love those - I always feel like a spoiled movie or rock star when I wear them.) I think both pairs were around $15, and of course they've lasted for months and months.