Due to the specialized nature of commercial projects, one size (or in this case, cost per square foot) does not fit all. After an initial discussion about the project scope, schedule, and other details we should be able provide a very rough assessment of cost. The accuracy of any cost discussion is directly proportionate to the amount of detail that can be provided. A phone call is generally enough to provide a wide range square foot cost.
For information on the process of building and opening a restaurant check out this post.