While a custom wedding dress by Vera Wang can run you tens of thousands of dollars, a custom wedding dress from a non-famous designer can cost a lot less. I remember looking into having my wedding dress custom made my a dressmaker who worked full-time at Vera Wang and the price of the dress she was going to make me was a quarter of the price of the Vera Wang version.
If you're having trouble finding your dream wedding dress you may want to look into having a professional seamstress/dressmaker design and make your dress.
But how do you find a reputable person? You can ask friends and search local wedding directories online and in local wedding magazines. You can also do a Google search but if you find someone through a Google search you should thoroughly research that person/company via non-Google methods.
Always check references and ask to see a portfolio too.
You have to truly trust the person you hire to be able to create your dream wedding dress and if you're not 100% on the idea then keep visiting local salons and order a dress you find there. It's not worth risking $1000+ and your peace of mind.