As one of its daily deals, Sir Macho offers this 2-Liter Bicycle Mouth Hydration Bladder for $9.99 with free shipping. Outside of the mention below, that's the lowest total price we could find by a buck. Made of high-grade TPU, it's crush-, heat-, frost-, and mildew-resistant. Deal ends May 26.
A close price: Tomtop.USA via eBay charges $10.04 with free shipping.