Newegg offers the refurbished ASUS Gigabit Network Adapter, model no. NX1101, for $10. This $10 mail-in rebate cuts it to $0. With $1.99 for shipping, that's $17 under the lowest total price we could find for a new unit. It features data rates of 10/100/1000 Mbps and is compatible with Windows only. Deal ends August 2.
A 90-day warranty applies, but it is unclear who backs it.