Interesting idea. I suppose just a duffel-bag or a steamer trunk would be too horizontal? You want something specifically for hanging?

How about a wardrobe box from U-haul? It would be quite cheap, and you could probably make it more durable with some duct-tape (or better-looking Gorilla Tape) to cover any of the cardboard edges that would wear with repeated use. If you don't like the U-haul branding, you could 'gift-wrap the whole thing, or maybe just cover it with butcher paper.