Alvin Valenta, Lazaro, andVera Wang all make beautiful, formal bridesmaid dresses which you could wear as a bridal gown. For non-weddding brands, BCBG, Betsey Johnson, and Laundry all make gorgeous dresses in good colors.
Fall, where are you from? Just go shopping and have fun, you have the most minimal limitations. I'd check out the fashion district in a bigger size city, or department store dress sections. (sometimes JC Penney awes me.) What do you plan on doing with your hair? Are you wearing a headpiece at all? because you could get a great hat, or custom headpiece by a milliner. Check out the dresses worn to awards shows by celebreties for gown inspirations. In style magazine usuallly has a great spread of gowns.
My friend bought an ABS gown for her second wedding. It was bronze green and a copy of Hillary Swank's first Oscar gown. It was gorgeous and didn't cost her more than a few hundred dollars. myra at www.classysassyweddings.com