How do I come up with a monthly budget for a 6500 sq ft, family restaurant

6,500 sq. ft. is a really large space for a restaurant! For one thing, you start with a business plan. Do you already have one? If not, then you could try the following searches.

Family Restaurant Business Plan Budget - Google Search

Business Plan Figuring the Budget of a Restaurant - Google Search

Restaurant Budgeting Business Plan - Google Search

Other places to find sample business plans that you could tailor to meet your needs would be http://www.sba.gov/ and SCORE | Counselors to America's Small Business | SCORE