You may find that paying a human for a ticket incurs a booking fee whereas paying your computer for the ticket avoids the booking fee. It is rare (IME) for cheaper prices in airline offices. Web sites such as expedia may have cheaper prices, but let the buyer beware. Personally, I'd book now so I get a seat on the day I want to travel rather than wait in hope for a change that may not happen - indeed may push you into a higher fare category because someone else got in first.