Dress Ruminations

Since I have two weddings in October, I had decided to buy a new dress. But now I'm considering getting an old bridesmaids dress altered and dyed instead. The one I have in mind is a perwinkle floor length dress with a chiffon skirt that is about 2 sizes too big for me. Not only will I get the dress taken in, I will get the skirt shortened to knee-length. I would love to dye it deep purple too but I don't know where I could get a dress dyed, if a month is too little time and what order should I do: dye then alter or alter then dye.