Here's a gorgeous long backless halter prom dress with dramatic details. With a deep v-neckline, this long formal dress has halter straps that attach above the open back for a sexy vibe with every turn at prom, fancy galas, and other black-tie events. In misses and plus sizes, this elegant long evening gown has ruching at the waist for a long, lean look and a side sash that adds the drama. The hip-skimming long skirt has a thigh-high side slit that completes the look of this long backless halter prom dress that is surprisingly priced under $200.