I would think that a art portfolio would be great for that.  They don't cost much and you can get them at most art stores.  They come in many sizes, 8.5x11, 11x17, and larger.

 

The portfolio is like a large photobook, with soft plastic covers and plastic pockets inside.  The front usually has a full size pocket as well so you can make a sign for each portfolio to catigorize the items. 

 

You can also put stickers on the plastic for pricing, and peal it off to change the price in accordance with the fair or show your selling in.