In Nanjing, there are a lot of "hole in the wall" places that perfectly accept WeChat/Alipay indeed, but as said, probably depends heavily on the city.

To OP, it depends massively what and where you'll be eating.

You can easily eat out (reasonable, not fast food..) for less than 200 RMB per person (breakfast, lunch, and dinner) - that would be either included breakfast at the hotel or a snack (like those wheat/omelette sellers who make you that goodness snack on the hot, round plate), then for lunch some place with a lunch meal (around 40-50 RMB most usually), and a dinner at a restaurant / at a place in a mall for around 150 RMB (for example, a lot of hot pot including beer at places like "Little Lamb/Sheep")

http://www.littlesheephotpot.com/ (they expanded even overseas, and the menu is in English as well)

That said, of course you can go splurge and spend 1000 RMB if you feel like it.. China isn't much different than any other country. Or you can cut it and easily feed yourself with tasty stuff for less than 50 RMB per day (2-3 Baozi for lunch, Halal noodles with meat and vegis for dinner for example..)