Topic: Open RFID Tag
Hi!
Check this project:
http://www.t4f.org/projects/open-rfid-tag
It is an universal programable RFID tag for low frequency readers.
It can be used to implement different RFID attacks like clonning or brute-forcing and it can be build for just less than 12 euros.
Schematics and firmware are avaliable in that web!