The easiest thing to do is check the C. B. Gitty Crafter web site you can get some fairly cheap pick-ups there, I think they got some pre-wired things for under $15 if you don't won't to do the soldering yourself... They got a few different kinds including single coil pick-up and Piezo Transducers. pick-ups.
I think the Piezo Transducers are great and if you want to do it all yourself (that is the real fun of this after all) Go to Radio Shack ask for the 273- 073 Piezo Transducers get a little bit of wire a 1/4 jack and some duck tape and you can get a cool sound.

it's all about experimenting....when I go to Radio Shack I usually get whatever Piezo Transducers are not sold out.... 273- 073 seem to work just fine... and the CB Gitty website always have bulk deals on Piezo Transducers....the one thing you might want to do that I don't really show in these pictures is muffle the piezo by placing it in between some foam or thin pieces of wood to prevent feedback