piezo conductor - I got 5 for a buck on Ebay.
Wires - I recycled mine from a toy but insulate copper wire is cheap.
1/4' stereo jack - another dollar on ebay but you can get them in lots of 3-5 for the same amount.
clear plastic container - I used an old peanut butter container but really, anything works.
Soldiering pen and skills. Self explanatory.
Red wire goes from middle part of piezo to the contact for the long piece on the stereo jack. This is the + hot wire. The black wire goes from the outer ring of the piezo to the other contact on the stereo jack. this is the - ground wire.
I drilled a hole in the side of the container for the jack and the bottom for the contact mic, then attached them. Its a rough piece but its a prototype. Now you just plug a cable into it, connect your recording device, and go!
You can see it in action here: