Ebay offers Embark Backpack Hydration Pack Hiking Camping Cycling Bladder Reflective Blue 4L for $11.99 (reg. $39.99) with free shipping. 

Product Description:
This 4-Liter Hydration Pack from Embark makes it easy to stay hydrated while camping, hiking, cycling and beyond. Featuring a water-resistant construction for lasting outdoor use, this small hydration backpack features a padded shoulder strap plus a sternum strap for easy, comfortable carrying. A two-liter hydration bladder sleeve with a tube straw allows for hands-free drinking, and the main zipper compartment plus an exterior zip pocket give you plenty of space for all your outdoor essentials. It also features a ventilating mesh back to help you stay cool plus reflective details that make you more visible in the dark or during inclement weather.