Chief, how do you expect anybody to stay in business if all they do is charge for their specific job-related expenses? You eat, have a roof over your head when you sleep, have a dry place to work, enjoy a vacation now and then, and even put a little money away for retirement, right? You don't get to have those things if all you do is cover the cost of the task at hand. Why would you expect a mechanic to do it? What about all the down time that the guy has to absorb while he waits for somebody like Bad O. to come in with a problem to fix. $181 sounds like a bargain to me. It certainly doesn't cover an hour of my time and I charge extra for expenses.
Bad O, there are a number of potential reasons why you may be over-doing the oil. The obvious is that your math might be wrong when you calculate the amount of oil to add. Or, you might not be draining all your gas. If you routinely fill your tank utilizing those pre-determined oil mixture bottles and you have gas in the tank when you do it, the oil mixture slowly but steadily increases. Also, if your outboard runs on 50:1 and you are not careful, you might be adding the contents from those small bottles that are sized for 40:1 based on a pre-determined fuel capacity.
Not reading the label got me in trouble when I filled my wife's leaf blower one day. She was buying those bottles from Sears and Home Depot that have the gas and oil already mixed at 50:1. She also had some of those little bottles that were just straight gas. A day after she got her leaf blower back from servicing at Lowes, I added straight gas from one of those bottles, by mistake, and gave her the blower to use. 5 minutes later it crapped-out and she returned to Lowes in a huff to complain about their service. They figured out that the straight gas broke the motor and she returned from Lowes with a new leaf blower ... and she cursed me out with some pretty salty language when she got back. The original service probably cost $250 and then she had to buy a new leaf blower after all. I hate those damn things. I can't stand the noise and the oil-rich smell of the gasoline, either!