You are absolutely right. Cheap sunglasses do not offer complete UVA & UVB protection. Cheap sunglasses block some light and allow your iris to open, which increases the exposure to UV rays. While you don't need to spend $200 on a pair of sunglasses, just make sure to ALWAYS purchase a pair with 100% UVA and UVB protection. If you don't, you are a fool. And Herman, typically when one purchases a pair of $200 sunglasses, they tend to make sure they do not lose the $200 pair of sunglasses.
My eyes get real sensitive to sunlight when I have my contacts in. $200 on a good pair of glasses is well worth not getting migraines.