Kristin Lyn Crase and I made this Simplicity 4055 pattern in a weekend. The pattern went together relatively easy, if I remember correctly.
Of course actual regency attire is not necessary. Any floaty skirt and tiara or for the women or button down shirt and pants will work for the men (although vests and jackets really add to the proceedings). Feel free to gender self identify. If you purchase one thing for the evening, I would recommend gloves. They make every thing feel old timely and genteel.