There aren't any really cheap options other than self catering, as there aren't any chain fast food joints. However, you can eat well inexpensively, at the bakery, the pizza joints, and the pubs. For a decent meal, the Chinese restaurant in the main street (Shanghai Palace?) is fantastic, and great value.
On-mountain lunch options are few, and very expensive. If you are staying in town, it's inconvenient to go back to your accommodation for lunch, so plan to pack a lunch or have a big breakfast and just a snack during the day.
However, if you do want to stop, the Skiers Union in Mountain Village is (relatively) cheap with great food and atmosphere.