You can browse it online at ebay.com or amazon.com by stylish brands sunglasses under $ 100. Or you can looking for some cheap , stylish yet good quality sunglasses at some optical shop like Firmoo.com.
Here is my method to get stylish brand sunglasses under $100: Find designer sunglasses coupons that some people share on certain websites. It can save you a lot. I often get coupons on retailmenot. You can have a look at the site.