Newegg via eBay offers the TP-LINK 802.11n Wireless 4-Port N300 Broadband Router, model no. TL-WR841ND, for $17.99 with free shipping. That's $2 under our April mention, and aside from the mention below, the lowest total price we could find by $4. It features two detachable antennas.

A close price: Next Warehouse has this router for $18.54 with free shipping.