Here, I found an authentic one on ebay. Compare this bag to the fake one... you'll see the differences.
AUTH LOUIS VUITTON CRUISE CABAS GLOBE SHOPPER MM TOTE - (eBay item 120154528776 end time Sep-02-07 15:52:16 PDT)
There's nothing wrong with trying to find something cheaper on ebay, you just need to be careful. Make sure you know the item you are looking to purchase. Go to an LV boutique and examine one in person... make notes of the smaller details. And remember, you're never going to find an authentic LV bag on ebay for WAY less than the retail price... its just not going to happen. If something is super cheap its most likely a fake.