In order to find a gown for less, you have to be a little flexible. I rented my wedding gown, and I got a great deal (gown, detachable train, veil, headpiece, petticoat, alterations, and cleaning all for $850). Plus, I didn’t have to worry about storage afterwards.
You could try renting, or if possible, borrowing a gown from a friend (one of my friends gave her wedding gown to another friend, and with slight alterations, it looked perfect).
David’s Bridal is a great place to start if you choose to buy.