A better way to look at this is to figure out what it costs for your truck to just sit in the driveway/shop. Figure out what all and I mean all of your monthly expenses are from business to mortgage, health insurance, property taxes etc. and divide that number by 365 to get your true daily cost. Lucky for me my houses, equipment, trucks, and everything I own is paid for. My overhead is low but I still have plenty of taxes, phone/internet, maintanence, insurance, business supplies, etc to pay for. My biggest expense every year is fuel. Now that I have implemented a 20 dollar trip charge that is not an issue anymore. I just explain to my customers that I am an independant contractor and I can buy any tool or piece of equipment that I want and I choose to use the best. Sure I could show up and clean with a small truck or portable but since I choose to run a larger more powerful system I have a 20 dollar trip charge and will raise it to 25,30,40 etc over the years as fuel prices and chemicals go up.
