Well...these don't look like competition dresses that I would wear to a comp like Nationals, Emerald or Ohio Star, etc.. If it's Fred Astaire or AM in-house sure you'll be fine. If money is tight rent a dress and seriously try something on...at least a sample before you actually buy something. Wait until a major comp is in your town or close by and go try some dresses on.
You also don't want something that is no longer in style because it makes you stand out and not in a good way. This is again not an issue if this is an AM or FADS event.