I just went Prom shopping with my DD yesterday. (Visiting relatives in Houston. For spring break) Based on a suggestion on this board we did got look at Ross. There were several short dresses that would have worked for some girls bu my DD was too tall for that particular style. We found one Halter style dress that fit very well, but the color wasn't right for her. If we were on a very tight buget it definitely would have been worth driving around to the many Ross stores in the Houston area to look for a dress.
We ended up getting her dress at a place called Formal Gallery on the west side of Houston. It had a huge varity of dresses and prices. Some dresses were as low as $59. We spent $205 which included the dress, shoes, jewelry, alterations, and shipping. They do have a web site where you can order.