The offer of places to eat in Sapa is quite varied. It won't be difficult to find a place that suits your tastes. On the walk from your hotel to the market you will see many restaurants. Prices are somewhat more expensive than in the rest of Vietnam, but still a real bargain.
For a real Vietnamese experience, try the soup noodles (Pho Bo or Pho Ga) at first hour in the morning. A Bun Cha (meat balls) or some Nems (Vietnamese rolls) for lunch, and a vegetable salad for dinner. And nothing tastes better than a Vietnamese Beer after a hard day trekking ...