As one of its daily deals, 7 Deadly Deals offers this Nylon Boonie Hat with Rear Sun Flap in various colors for $8.99 with free shipping. That's $6 under the lowest total price we could find for any boonie hat. It features a drawstring that tightens the headband for fit. The color is chosen at random. Deal ends June 13.
There's a less expensive way, and then there's the way that works for you. The two may not be the same.