I bought my wedding dress from ebay for only $50.00! In fact, I bought two just in case I didn't like one, the other was for $50.00 as well. My dress retailed over $900. I spent more money getting it altered than what I actually paid for the dress. When I told the lady who was altering my dress she could not believe how much I paid for it! I would not have been able to purchase the material alone for only $50.00.
How it was explained to me was that a wedding store was getting rid of some of it's inventory. The dress I actually wore for my wedding was a dress that was displayed and then tried on at times. It was NOT used, just used as an example.
I was also told that many wedding stores get sent "samples" at no cost. So when you see a dress listed at a really low price, chances are they didn't invest any money in the dress itself.
I've been really lucky with ebay. Just read the feedback, I did.
Good luck!