TomTop offers this 3.5" TFT CCTV Camera Monitor Security Tester for $32.99. (Choose "US" as the plug option.) Coupon code "SCM316" drops it to $29.99. With free shipping, that's the lowest price we could find by $10. It includes a wrist strap and allows for audio testing.

Note: This item ships from China and may take up to two weeks to arrive.