Your wallet is about to feel a pinch the next time you book a flight. A new airline hidden fee is rolling out that automatically charges you for seat selection, even if you skip it, adding $10 to $50 per ticket. Travel experts warn this could cost a family of four an extra $200 on a single booking, hitting your summer vacation budget hard. Avoid the charge by booking directly on the airline's website and unchecking that box during checkout—before it's too late.