REI Garage offers the Timbuk2 Medium Strap Seat Pack in White or Diablo for $10.73. Opt for in-store pickup to dodge the $5.99 shipping charge. That's tied with our mention from last August and the lowest price we could find by $7. It measures 6.5" x 3" x 2.2" and features a keyring tether, hook-and-loop strap, and durable ballistic nylon.
eBags via eBay offers this Traveler's Choice Rome 20" Hardside Rolling Carry-On in several colors (Gray pictured) for $39.99 with free shipping. That's the lowest total price we could find by $6. It features a telescoping handle, tie-down straps, and internal pocket. It measures 21" x 15" x 9".