How much should you charge for fruit feeding 150 people?

You need to know the cost of the fruit plus the number of hours it will take to cut it up or otherwise prepare it. You may also need to consider providing serving trays and utencils. Pay yourself a reasonable rate ($10/hr??) for this, add any transportation costs and then add 10%. Keep in mind that you may be compared to what a grocery store would charge for a fresh fruit tray, unless you are making a creative presentation.