REI Garage offers the Avenir Presta Valve Bicycle Tube for 73 cents. Choose in-store pickup to avoid the $5.99 shipping fee. That's a buck under our mention from a month ago and the lowest price we've seen. (It's also the best deal now by $7.) It fits 26" wheels.

Of note, a similar tube with a Schrader Valve is also available for 73 cents with the above shipping options. That's also a buck under our mention from a month and another all-time low.