I've managed to source short film costumes from theatre costume closets a few times now -- it's a great bargain for well-made, extravagant and professional pieces.
The Seattle Opera is having a costume sale TODAY to clear out their closets and I got a peek at their selection earlier this week. There are a TON of great costumes, many of them in sets. If any of you fellow filmmakers are thinking about shooting a period piece, I urge you to come check out the racks. From what I saw, they have gorgeous gowns, armor sets and plenty of on-theme costumes suitable for extras at around $20 a piece, being offered for the first time for today only.
Enter at the door at the corner of Terry an Thomas St., not at McCaw Hall. Cash or Checks only -- no dressing rooms, so come prepared to try on costumes on top of your clothes.