Here's a good price.
http://cgi.ebay.com/ebaymotors/_Car-Truck-Parts-Accessories__2-2004-2008-FORD-F-150-TRANSPONDER-PATS-KEYS-OEM_W0QQitemZ360118397485QQadiZ2865QQadnZCarQ20Q26 Q20TruckQ20PartsQ20Q26Q20AccessoriesQQcmdZViewItem QQptZMotors_Car_Truck_Parts_Accessories?hash=item3 60118397485&_trksid=p4506.c0.m245&_trkparms=72%3A5 43|65%3A12|39%3A1|240%3A1318