Green Industry has the right idea; base rate for 4000 sqft. Add a charge for each additional 1000 sqft. Suppose it costs an average of 1 dollar for materials,(averaged over the year), and 2 dollars for the labor and equipment to apply the materials. The base rate includes a charge for overhead, postage, insurance, rent; Suppose overhead was 5000 last year, and you did 5000 applications--you would charge$1 per application included in that base fee. The base fee also usually includes about 10 to 15 dollars for the cost of driving the truck out to the house, (for gas, truck payment, and your labor to drive).