I'll be transiting through Shanghai on the way to London and have an 8 hour layover bright and early in the morning. I'm planning on getting cash from the ATM at the airport for the day, but am not sure how much I'll need. I really want to avoid getting too much out and needing to reexchange it later. So, how much do I need for two people to take a taxi into the city, eat street food and/or a cheap meal, maybe pick up some candy or other snacks for the plane, and take the subway and maglev back to the airport? Are there any hidden costs, like airport departure fees or anything? Thanks!