Continental 42mm Presta Valve Tube
700 x 20-25cc
$5.63 shipped / amazon prime... If not prime holder, need to spend $35 for free shipping.
Not sure if killer deal or not, but I usually spend $7.50 for them here.
Amazon.com : Continental 42mm Presta Valve Tube, Black, 700 x 20-25cc : Bike Tubes : Sports & Outdoors