I go by the linear ft on these types of buildings and then look at the cost of labor, chemicals, fuel, and so on. If I start with .10 cents per sq.ft your only looking at 586.00 for the job. Depending upon the cost of 12% in your area it could be 1.50-4.00 per gallon and you may even have to use it straight to get that off. So say you need 30 gallons of 12% at 2.50 per gallon and thats gonna cost you 75.00 plus fuel, labor, and maintenance. If you spend 20.00 on fuel, and have no helper and figure 25.00 for maintenance your looking of a profit of 486.00 for the job. In my opinion that job might take anywhere from 2 hours to 8 depending on the results you are seeing.
this is how i approach most jobs to ensure i am not getting myself into something i priced too low or way too high. What do you think yourself?