If you've only ¥16 to your name and you're half-starved, hand your cash over to the staff. For ¥16 to ¥18 you can get a vast steaming bowl of rice noodles with copious amounts of chicken, beef, pork or fish thrown in. The fish noodles (水煮鱼片米线; shuǐzhǔ yúpiàn mǐxiàn) in particular is superb (watch out for bones); free refills of noodles available.
There are three degrees of spiciness: slightly (微辣; wēilà), moderately (中辣; zhōnglà) and full-on (香辣; xiānglà). It's not a hole in the wall and is pleasantly designed with blond wood and grey brickwork. Packed at meal times.