For truly unique styles, I designed my Year 10 and Year 12 formal dresses and my mum made them. My Year 10 one is like the late-1800's ball gowns - Blood-red satin with faintly printed flowers, three layers of off-the-shoulder satin wave-frills plus a string of studs around the shoulders, a flower on the hip, a split down the left side to reveal a second layer and another round of wave-frills at the bottom . You really feel like a princess wearing one of these...
...But it was a bit over the top and so my Year 12 one was simpler and more modern - Swimming pool blue satin, mermaid shape, off-the-shoulder, scruched-up blue chiffon around the shoulders and straight down the back clipped by a brooch, two asymetrical columns of single studs running down the body to the knees, a string of studs around the knees and another brooch in front of that - It had a royal feel to it, like it can be worn to palaces and such.
Both dresses cost less than $200, buy the fabrics at Cabramatta - there's a bridal and evening gown fabric shop on the main street. The accessories were a bit expensive and it took around two weeks to sew...but they're the best dresses I've seen so far.
My point is, try have a vision of your dream dress, my vision always has a princess feel to it. You don't have to, just ask yourself what style you like, colour etc...HARTS always has the best dresses, and the price range is enormous...go there
One of my friends bought hers in the QVB, cost her $800 and was voted "Best Dressed" - It was peach, short, low-back low-front and had sequins all over it....So, make it if it's possible, it's way cheaper and no one else will ever wear that dress...there's no risk and that's truly unique.