The good girl will always be cool and "in". No wonder the french say "c'est tres BCBG"..which would mean: "you've got such good taste/style." Good, rich girls almost always have great style..but it doesn't mean that everything you wear - or anything - has to be incredibly expensive..
A little BCBG for the beach? A few summers ago I got a Borsalino straw hat for a real bargain price..and since I suffer from sunstrokes during the summer I almost never take it off. To get the best of Italian sun you'd definately have to wake up early..preferably with a cappuccino freddo-latte macchiato freddo-caffe freddo-caffe al vetro-macchiato freddo while reading your horoscope and the international news (who gives about Italian politics) from a newspaper, and hit the beach with a souvenir Saint Mary bag from Playa del Carmen, Mexico...and a less than 10euro black string bikini..and a little more than 10euro sunscreen.
This way you're doing what Aristotle taught us: "To be successful, keep looking tanned, live in an elegant building (even if you're in the cellar), be seen in smart restaurants (even if you nurse one drink) and if you borrow, borrow big."