Bocata is one of my favourite places in Beijing for sandwiches. The environment is comfortable (outdoor seating in the summer, nice clean bathroom), the prices are on the low-end of the expat pricing scale, and the food is spectacular.

I've tried a good number of their sandwiches, and they're generally all extremely well done, and the french fries are an almost necessary accompaniment. Service does not tend to be as annoyingly obsequious as so many other expat dining places here in the 'jing.

A sandwich, a drink and a few french fries will fill you up for the whole day, most likely for less than 50 RMB a person.