Newegg offers the refurbished HP 120-watt 4 USB PLT 1.0 Docking Station, model no. KP080AA, for $10. Redeem this $10 mail-in rebate to drop the price to $0. With $1.99 for shipping, that's $37 under the best we could find for a new one. It features one AC power port, audio in, audio out, DVI, and one external monitor port. Deal ends December 30.
A 90-day warranty applies, although it's unclear who backs it.