Amazon offers the Nintendo Official Elite Transporter Case for 3DS for $15.99 with free shipping. That's $19 under the lowest total price we could find for a similar case elsewhere. Sales tax is added where applicable. It features a carrying handle, secure flap closure, and external zippered pocket.

Update: Note that this item is temporarily out of stock, but can still be ordered at this price for delivery when available.

Update 2: It's back in stock.