i don't know where you get that pricing from. Mark up price for sunglass are 2 times only. A friend of mine close down one of his optical shop and need to move out his old inventory (if you wonder). The price i can get for you is his "WHOLESALE" price. Typical mark up is 2x. Other place can mark up to 5x.
Just go to any private OD office and check their Gucci sun and you will see most of them sell for around $300. $700? you shop at Hollywood?
All the model i refer to is from the link above. Just check before you barking. I don't need to pull any trick here.
Do me a favor, go check price on these at any optical store in your hometown. ;)