ShengeHe-US via Amazon offers the Anbes 4-in-1 Wall Scanner for $28.99. Clip the 20% off coupon on the product page and apply coupon code "5GALZCKI" to cut that to $8.69. With free shipping, that's $20 off and the lowest price we could find. It features 4 detection modes, LCD display, and automatic calibration.

Update: The clipped coupon is no longer available, yielding a price of $14.49.