RueLaLa is featuring evening dresses right now, some of which could make beautiful attire for BMs or MOB/MOG. Their sales only last a couple days, so if you see something you're interested in, you have to act fast. I've yet to order anything from them, so I can't vouch for customer service, but their return policy is stated clearly on the site. Here's a link:
Fyi: I get some sort of merchandise credit should you join RueLaLa and make a purchase using this link, but I'm not posting it for that reason. Hope this saves someone some money!
"Do not fear, for I have redeemed you; I have called you by name; you are Mine!" (Isaiah 43:1)