J.Crew offers its J.Crew Women's Sophia Wedding Gown in Ivory for $199.99. Coupon code "STYLE40" cuts it to $119.99. With free shipping, that's $305 off list, the lowest total price we could find, and a very low price for such a dress. It comes in sizes 0 to 4. Deal ends August 4.
Note that these items are non-refundable under any circumstances.