Honestly, I think it is this sort of perspective that is really killing America, and what it can be. What you are citing are not hidden costs at all, but rather imaginary costs.
The labor the wife and I put into the access road was indeed zero because there was no cost. We can arbitrarily assign our time a number, but any number given is not accurate, just justification for doing it. But we do work for free, all the time, we are farmers. We could take our gross earnings in a given year and deduct how many hours we worked to earn it, yet that number would be microscopic on a per hour basis. In fact most farmers would. But the reason we do that is because you are confused between assigning something a number and something called lifestyle. It probably is the reason why 1/2 a percent of this nation happens to feed the other 99-1/2%. If we calculated our costs as you are, we would all conclude we are losing money. The truth is, we are not, just because we are not making money, does not automatically mean we are losing it either, so the real question is, is it worth doing, and that does not need a dollar sign in front of it or not to be answered.
You are correct in that there was some fuel used, but not a lot...but to your credit some, but wear and tear I always have a problem with because time is the worst enemy of any equipment, the absolute worst thing a person can do to any piece of equipment is park it and not use it. Sure usage wears on the unit, but so does just parking it.
As for the gravel, that again was truly a zero cost because gravel is pretty resilient, all I did was move it from point A to B. It is still on my property, just not in a gravel pit, but spread out upon a road. Since it does not wear out, nor change, I could scrape it up and resell it if I wanted too. I cannot see for the life of me how that has a cost.
So in review, we have $50 spent in fuel for a $13,200 project, but that is not really accurate either because by your own strange rules, I can just say it was zero dollars because I had allocated $50 in the forestry budget for forestry operations that I never utilized. That extra fuel I used to build my road and was already in my overall farm budget.
I am not trying to be snarky here, I am just trying to show that when you get into numbers, it is very easy to manipulate them. We have to be careful of that.