VFA&W via Amazon offers the Angelcare Movement & Sound Baby Monitor, model no. AC201, for $30.94 with free shipping. That's the lowest total price we could find by $34, outside of the mention below. It features a 326-foot range and an under-the-mattress sensor to monitor baby movement.
Note that new customers at Groupon can score this for $18.99 with $3.99 for shipping via coupon code "WELCOME."