This link will take you to their "Optional Service Fees" -- about halfway down the page there's a selection for Seats/Upgrades ... $5 - $99 per seat depending on location...

http://www.usairways.com/en-US/trave...taxesfees.html

That said, during our past trip we chose not to do pre-seating (either direction) and took our chances with check-in at the airports. It worked out just fine and we paid nothing additional... Our flights were with American Airlines, but I think the same applies... - k