Sundress (São Paulo)

I am going to a wedding in Vermont on very short notice, and have had lots of trouble finding a dress here in SP! Everything I have found here is either way too short (I'm 5'11") or too formal. The wedding is in rural Vermont, during the day (and of course, it is summer there). I'm looking for a more basic (conservative by Brazilian standards) sundress that doesn't cost an arm and a leg-- anyone have any suggestions on where to look?

Thanks!