Ebay offers Embark 20L Hydration Backpack for $19.99 (reg $49.99) with free shipping.

Product Description:
Stay hydrated as you hike, climb or cycle with this 20-Liter Hydration Pack from Embark. Featuring a water-resistant construction for lasting outdoor use, this 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 a spacious 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.
Embark: Find wonder as you wander.

• Dimensions (Overall): 19 Inches (H) x 10 Inches (W) x 4 Inches (D)
• Weight: 1.59 Pounds
• Suggested Age: 18 Years and Up
• Shell Material: 100% Recycled Polyester
• Bag Structure: Softside
• Interior Features: Hydration Bladder Sleeve
• Exterior Features: Airflow Back Panel, Zip Pocket, Padded Shoulder Straps, Reflective Tape, Sternum Strap
• Main Compartment Closure: Zip Closure
• Fabric Name: Pressed or Molded
• Capacity (Volume): 20 Liter
• Garment Details: Polyurethane Coating
• Protective Qualities: Water-Resistant
• Used For: Camping, Hiking, Climbing, Bicycling
• Maximum Strap Length: 30 Inches
• Fits Laptop: No Laptop Pocket
• Minimum Strap Length: 17 Inches
• Battery: No Battery Used
• Care & Cleaning: Spot or Wipe Clean