Parts America online (Kragen/Checkers/Schucks/Advance Auto) at
http://www.partsamerica.com shows they carry left and right replacement headers. The left side is about $84 and the right side is about $117. You'd still have to add shipping & handling plus tax to that. Your local store can usually order them if they don't have them in stock. The price comes out about the same either way. You can also check the following:
http://www.napaonline.com
http://www.oreillyauto.com/B2C/vehicle.ecatalog
http://www.carquest.com
http://www.autozone.com/
Just go to any of these sites and put in your vehicle information or locate your local store and call them.
Good luck.