S.L.
i'd break out the black dress or good cocktail dress as well! just make sure it doesn't scream "i was bought in the 80s" with shoulder pads or too many sequins. simple details and accessories can dres up a great solid color dress. think great shoes and a pearl necklace.
also, you don't need to go broke if you don't have one. think t j maxx, ross, or resale/consignment stores. there are name brand deals to be found in all sizes!