I can't give an actual accurate price or place, but go thrifting! You always find designer stuff hidden in those places. One of my close friends has found quite a few designer bags thrifting pretty cheap. I always see them when I go thrifting, just never buy cause bags aren't my thing.
Well it depends. You can check ebay, or craigslist. They usually have them in great condition. Thrift stores may have them But they arnt usually as high quality. But if you find some other site double check to avoid scams.
Or the flea market/swapmeat !