Is it worth buying expensive sunglasses for lifeguarding on the beach?

I am a new lifeguard working out on the Gulf and most of the lifeguards have expensive sunglasses. I have polarized sunglasses from Walmart, but they aren't the same quality as, say, the Costa Del Mars. I was just wondering whether it is worth buying expensive sunglasses, if there is a chance I will lose or break them working on the beach. And if they are worth it, could someone direct me to a website that has them for cheap?