Uh, oh! This is a loaded question to a home remodeler. Cost per square foot is impossible to calculate before the layout of the room(s), quality of materials, fixtures and appliances are settled on. Just selecting a certain price range of kitchen appliances can change the project cost significantly.
It makes more sense to focus on the cost to construct in discussions. This can be revised based on the clients personal choices, complexity of the remodel, etc. Perhaps a more important number to use is the clients budget, minimum to maximum amounts. Then the remodeler can show the client what is available in materials to meet their budget constraints.
During the design phase, for instance, a more expensive granite countertop could be replace by a clients wish for a high quality gas stove. There are numerous trade-offs, and a good experienced contractor will know what less expensive material will look as good as the clients first choice product.