Yay for robes, but not bathrobes! - nice, sturdy choir-type robes that you could order from your HQ or Robes R Us.
They could be passed down through the chapter and a "robe fund" maintained as part of local dues for when they need replaced. The best part is that no one would be dressed inappropriately. I've seen various "whites" in person and in pictures, and suffice it to say I would be embarrassed to stand next to some of these people in a club, let alone in a ritual.
It is very, very very hard to find white dresses sometimes...but in dire circumstances, I think I would prefer a white t-shirt & white sweatpants to a bedsheet, or someone dressed like a whore.
If it's between the whore and the bedsheet, I pick the bedsheet - at least your butt isn't hanging out of it.
Sorry, but I am a real stickler where this topic is concerned.
Oh, and yay, yay, yay for the schools who mention on their website that you might need a white dress - it's easier to buy it and take it back if you don't need it than find it at the last minute.