DailySale offers the First Alert Wireless Driveway/Intruder Alert, model no. SFA600RF, for $29 with free shipping. That's the lowest total price we could find by $1. It features transmission of up to 300-ft, flashing LED indicator, and the remote sensor detects movement.

Note: The countdown timer on the product page does not reflect an actual expiration time and resets daily.

Of note, Harbor Freight Tools offers a similar device for $16.99 plus $6.99 for shipping.