Box Guitar

a transducer.

a buzzer is something completely different.

i imagine you have just spent a total of something like 0-10 dollars making a homemade guitar and now you are looking at pickups and realizing they are like 50-80 for a decent piezo pickup. it is a bummer for sure. but they are out there somewhat cheaper if you look from them, but you will most certainly hear the difference. my cheap piezo kind of sounds like *ss. the other thing you could do is find a decent mic scematic and make an under the bridge mic pick-up. radio shack microphone elements are somewhat reasonable, but the sound isnt going to be as even string to string as it would be with a piezo attatched to the bridge.

good luck. feel free to email me if you have any questions. i'll answer if i can, i'm always making instruments.