Another thing thing to consider is renting a dress. I had a dress made for me and wore it 3x. I want something different now so I decided to sell the one I had made for me. Easier said than done. Since it was custom made for me, and I'm taller than the average dancer, it won't necessarily fit a big dancing demographic. The dresses for sale on this site seem to run on the smaller side - I'm a whopping 8, so keep in mind how long you will use the dress, how easy it is to re-sell if you want to, etc.
As for buying one overseas, I don't think I'd be inclined to do it. Part of the process should be having fittings done so you don't have to go and pay to get it re-altered, or find out that it doesn't hit your body where you thought it would, etc. If you're talented enough to transform/alter a dress, then it's probably not a bad option. When I buy a garment, especially a pricey one, I just want to be able to put it on and go....