I think one of your choices is to get sunglasses from Walmart. I have a pair of sunglasses bought there for $35 and they are in the third year now. Find a Walmart store near you and go to have a look. Another choice is to shopping online. Some discounted sunglasses are inexpensive and in good quality. You can search discounted sunglasses on Google.
The best places to get low cost sunglasses is, surely online shops. If you want to buy brands designer sunglasses in low prices, you can go framesdirect.com. They sell brands designer sunglasses at affordable prices. If you look more cheaper sunglasses, you can go firmoo.com, 39dollarglasses.com and glassesshop.com and more online shop where offer cheap sunglasses. My sister have bought a pair from firmoo and she said their sunglasses are good.