Get your hands on a murder mystery script (or better yet, write your own).
Create a business plan/proposal. Use non-union actors who will work for $1 to $2 per plate sold. (If you have an audience of 100 each person would make $100 to $200 for 2 to 3 hours work).
Unless you want to start your own restaurant, visit local venues. Stay away from any chain. What works best is a fine dining establishment in an old building or house. Talk to the owners and present them your business plan. Guests are willing to pay extra for entertainment. A cast of 5 at $2 per plate only raises the cost of meal $10. If the establishment owner charges $20 extra that's $10 pure profit for him (not to mention any additional sales throughout the night). Do Weekend only shows to start and go from there.
Cast. People are far more willing to audition when they know money is involved. Cast people age appropriate to the roles (no 20 year old playing a grandfather). Double cast just to make sure.
Self-promote. Tell everyone you know about your new venture. Drum up business.