need a "cheap" silver pinger

so watching all the posts with fake coins has made me a bit cautious as i like to buy loose coins at flea markets/yard sales, so i wanted to get a pinger to use when i buy them.. a pinger is a plastic clamp and a hickory stick.. it's not worth $35 on amazon or any silver vendor, i would rather spend that on more silver.

i need something that will last, does anyone have a makeshift/home made pinger design they can share?