TomTop offers the ATTOP YD-211 Phone Controlled Spy Tank for $39.99. Coupon code "TOPTANK" drops it to $31.99. With free shipping, that's $38 off list and the lowest price we could find. It features video streaming/recording, has a rechargeable battery, and is compatible with iOS or Android devices.
Note: The countdown timer on the product page does not reflect an actual expiration time and resets daily. Also, this item ships from China and may take two to six weeks to arrive.