There’s a great movie called the founder about a Ray Kronk the founder of McDonalds (well as we know it). He was struggling until someone explained that he had his business model wrong.
You are making the same mistake. If you want to run a business as you describe it, small regional stuff isn’t going to do it for you, it’s far too competitive and the margins are small. However, even without knowing the market you are in, the prices you are talking about are not feasible. Your example of a 400 dollar job with three people involved is pointless. In the U.K. a couple of speakers on poles will cost you £80 + vat (20% in the U.K.) if you pick them up. That’s about 160 dollars. Companies are paying 200 - 360 dollars for engineers. I would never supply an operator at my cost. Your 400 dollar job should be providing you with between 25-50% all day long. If it isn’t, look at what you are spending out on and work out what you need to be doing to change that.