What are the odds that job allows you to work an extra hour any time you feel like it? In the other direction, if you drop a few hours a week when you feel like it -- how long do you remain employed? Not too long, unless you're actually being underpaid for a specialist position.

Let's suppose that you have a salary of $200K/year, and the boss generally expects you to be working on the company's problems 40 hours a week, with the occasional flex time when you or they need it. Do they pay you more on weeks when you work 42 hours? Less on weeks of 38 hours? No.

(At lower salaries, overtime is real -- but a corporation is quite likely to fire you if you make a habit of taking or dropping hours without advance permission.)

Almost nobody is in a position where they can directly and accurately value an arbitrary hour as income or loss of income.

I pay someone to maintain my yard because I don't want to do it. I don't want to own the equipment either. It makes financial sense. So, even if I'm inside watching TV and hanging with my family, it's money well spent for me.

Some tasks may mean you can forego equipment purchases/maintenance but you're probably not literally saving money by having someone do something for you. Which is fine! It's perfectly OK to say I don't like doing yard work and can afford to pay someone to do it for me. You're probably both happier as a result.

We have to conclude that children, love, friendship, &c are all valueless because they do not have an exchange value ie: price.

There’s more to opportunity cost than money. That’s time with family, time to just chill, time for hobbies, all sorts of stuff.

Every time you pay to outsource a task you could do yourself by just putting in the time, you are explicitly saying “Having this time back is worth $X to me”. That is a direct measure of how much your time is worth to you.