Quantity   Component name
5 × Piezo disc $1.12 from fasttech.com
1 × Atmega8A $1.40 from ebay (I bought 5 pieces for $4.22
1 × A4 sheet of 120g black paper $0.29 at local store. I used Canson Vivaldi paper.
1 × A4 sheet of 240g white paper $0.49 at local store. I used Canson Vivaldi white n°1 paper
3 × meters of 30 AWG white wire. $1.49 for 10 meters on ebay. Single core is better. You can buy black wire, or use black marker.
1 × Cyanoacrylate glue (super glue) $1.0 at local supermarket
2 × CR2032 batteries $1.50 for 5 pieces on ebay
1 × Aluminimum foil $0. Ask mom.
1 × Paper glue or wood glue $0. You need few and probably have some, somewhere.
1 × Solder wire or solder paste $0. You have some.