Download a free murder mystery script from the Internet or write your own.
Host your murder mystery event at your home to save on venue costs and to keep it a private affair. Ask local social venues if they would waive the venue rental if you are organizing a charity event.
Cast professional actors for free by placing casting calls on casting websites, providing all job details. Recent graduate actors or resting actors struggling to find work may offer their services at no cost for a charitable cause. Ask members of your local amateur theater company if you can't get a professional cast.
Request to borrow, at no rental cost, period costumes and props from your local amateur theater company.
Send out invitations to your guests via email or hand delivery at least a month in advance. Ask guests to choose a character they would like to play and to come wearing fancy dress. Request that they bring along a bottle for refreshment and a food item for the murder mystery buffet. If it is for charity, mention this in the invitation and inform your guests that donations will be collected.