Now you see it. Now you don't. When you're airfare shopping, attractive prices can vanish in a split second. Just ask Jim Doll, a systems engineer in Atlanta, who recently tried to buy a ticket to San Francisco on AirTran Airways' Web site. He found a one-way fare for just $130, but by the time he'd toggled over to Orbitz.com to see if he could do better there and then clicked back, the price had changed.