I bought mine on Ebay, if that helps. But, I paid only $80 shipped for a dress that was $1000+ new. I bought it from someone who was selling several wedding dresses and it had been a store display or sample. If you want to unload it quickly, people aren't willing to pay a lot for a dress they can't try on. I was looking for one $100 or less shipped. In case it didn't work out, I would be able to afford another one.
After my success, my SIL bought hers on Ebay too, I think she paid around $200.
If you haven't tried Ebay yet, you may want to. It will get a lot of eyes that way.
The others had a good alternative - searching the weddingbee board seems good because someone might do it in several months or a year looking for that particular dress.
Good luck! I realized I was very attached to mine and paid more to have it boxed ($130) than it cost in the first place. It was my second wedding anniversary present from my husband.