REI Garage offers the Avenir Schrader 20" Bike Tire Tube for $1.73. Opt for in-store pickup to dodge to the $5.99 shipping charge. That's tied with our April mention, $5 off, and the lowest price we could find. It fits 20" x 1.375" to 1.5" tires and features a 35mm Schrader valve.