Beeebo-us via Amazon offers the Cacagoo Wireless Tire Pressure Monitoring System for $69.99. Coupon code "AKQUEUEB" cuts that to $55.99. (TomTop_W via eBay charges the same, although it ships from China.) With free shipping, that's the lowest price we could find by $2, excluding the below mention. It features an LCD screen, four external sensors providing pressure and temperature data, and real-time abnormal alarm. Deal ends January 14.

A close price: TTstoreusa via eBay offers it for $56.59 $53.76 with free shipping. (This item also ships from China and, like the above eBay seller, requires two to five weeks for delivery.)

Update: TomTop_W via eBay now offers it for $53.19 with free shipping.