I was one of those girls who shelled out around $500 for my junior prom dress. My parents paid up to $150, and the rest was on me to pay, but I had a part-time job and saved money for months. I have always been the type of girl who loves the big poofy ball gowns, especially when they're covered in sequins. And I had exactly that for my junior prom: a dress so poofy it didn't really fit in my boyfriend's car, completely covered in sequins, and I loved every second of it. I still wish I had an occasion to wear that dress again.
My senior year, my dad announced that I was not going to be allowed to spend more than $100 of my own money on a dress, which, when combined with the $150 he and my mom paid, left me with $250 for a dress. I ended up with one off Ebay, which was nice and reasonably pretty, but ultimately I liked my junior prom dress a lot more and still wish I had bought the dress I wanted that year instead of the dress I "settled" for. I will add that I had a part-time job at the time (and therefore my own money to spend on a dress), and I currently hold two part-time jobs, am a full-time university student, and am putting myself through college...and I still wish I had bought a dress that I really loved, even though that would have set me back a lot more money. At the time, I looked at all the online Chinese vendors and debated for weeks ordering from one of them, but I was too afraid of getting screwed over by one of them. My senior year in high school, I would have agreed with you one hundred percent...
There are SO MANY online sites --all with different names who say the will custom make your dress for about 1/3 the cost of the prom shops. BUYER BEWARE These are foreign sweat shops masquerading as legitimate options for a better deal on the dress you want. Two of DD's close friends got totally screwed last year by these "bargains" They shelled out 150. or so and the dresses came in the wrong size, rally cheap fabrics, and of course no one in China would return a call or take the dress back. They ended up having to buy another dress last minute and spending much more than they wanted to.
And then. My sister decided as a sophomore in high school this year that she wanted to go to homecoming, and she needed a short dress. She wasn't happy with the department store options, and she didn't want to spend much money, so she ignored my repeated warnings about the online Chinese vendors and went to
www.tidebuy.com. She ordered a gorgeous dress from them, got it in the color she wanted made to her measurements, and waited to see if it turned out. And boy did it ever! When the dress arrived, it looked exactly like the picture, except in a different color, and she looked fabulous in it! It was well-made, fit her perfectly, arrived well before it was estimated at. There was a decent return policy on the dress, so if there had been a problem she could have returned it, but with a dress as gorgeous as hers, she didn't need to. If I can find pics of the original dress she ordered and her in her dress (as the older sister, I wasn't allowed to take any pictures

), I will post them so you can see how well it turned out.
I know that these vendors don't always work out. Sometimes they really screw things up for people, and not all of them can be trusted. But many girls in our area order from Tidebuy, and Tidebuy always seems to come through for them. I know if I ever got to go to a prom again, I'd order from them in a heartbeat.
Here's the link if you want to give them a try:
http://www.tidebuy.com/c/Prom-Dresses-4354/
Your mileage may vary with them, but in my experience they've been a good company.