I have several pairs of identical Smith black choppers, and I live with them on. I have a pair with real glass lenses (they stopped making them in that frame several years ago) and two pairs with the synthetics. I use the good ones when I'm dressing up more, and the plastic ones when I'm banging around.
That said, I forgot my sunglasses at home and had to buy a pair at the Pop Century store before I headed out to the parks my first day. Were about $12 and very nice. I wish I'd waited until later, though, because I found a similar pair that had a discrete WDW logo on them I would have rather had.
Price isn't always an indicator of quality I have found, especially when it comes to sunglasses.
N.E.D.