Back in May, this post at Hackaday linked to a relatively easy to build RFID reader.
It looks like it would be somewhat inexpensive (less than $100) to build.
The trend towards putting RFID chips in credit and debit cards is a little disturbing, as its fairly easy and relatively cheap for an attacker to build even a simple longer range RFID reader. While this reader doesn’t read more than a foot away and doesn’t deal with the sort of encryption that should be on your debit cards (ha), its totally possible that an actual attacker could come up with something better.
To counter this attack, wrap your RFID cards or the inside of your wallet with aluminum foil. That should make it harder for a long distance reader to read.