You have to know your market, your cost and your ability then develop a price model and stick to it. If you are costantly beat do not get to down because there is competition. Hold your own and deliver and you will develop a reputation.
I just won a bid where I was 30% higher but I won on a score card including reputation and quality. It took me 7 years to develop the reputation. Under promise, over deliver and stay confident in your services.
FWI - $15.00 an hour does not truck, mowers, small tools, gas and marine insurance. Then you have labor and buden
Then you have profit.
I too have seen $15.00 an acre but that is for rough cuts on ROWs not parks and sports fields.