Kenneth Pool   New York Magazine Pick   The Gown: Tank A-line gown (back shot) with mauve and white floral and crystal embroidered bodice and butterfly-shaped train.   The Price: From $4,500.   Where to Buy: Gowns range from $3,500 to $6,500 and can be purchased at Saks Fifth Avenue, Bergdorf Goodman, Kleinfeld, and Wedding Salon of Manhasset.