ECmallUS via Amazon offers the Meterk EMF Meter Electromagnetic Field Radiation Detector for $47.97. Coupon code "X63834YA" cuts that to $29.74. With free shipping, that's $18 off and the best price we could find, outside of the mention below. It features an LED-backlit LCD, sound/light alarm, and range of measurements. Deal ends November 20.

Don't mind waiting a few weeks? You do? Well, just in case- bluelink88 via eBay has it for $18.34 with free shipping from China.