Arreglos - Vestidos De Fiesta (Help!)

Hi, ladies!

A friend of mine is getting married stateside first week of June and I still have to get my bridesmaids dress altered! Any suggestions of where to go?

So far I have only checked out a few places that do "arreglos de ropa" but none of them do "vestidos de fiesta". The material is silk (I think) and tull... so I have to be careful--but I don´t want to spend tons of money...

I live in Balvanera/Almagro area.

Any help is appreciated :)