I want my large lawn mowed. I put up a sign: “Mow 1 acre. pays $20.” I will get no one. Put up a sign that says “Mow 1 acre, $600”. I will get 100s of takers. So the trick is to set a price point FOR LABOR between $20 and $600. Get it LABOR IS A COMMODITY.
Now suppose they get themselves hurt while working on your property (by stepping in a hole and twisting their ankle, for example). Congratulations, you've now opened yourself up to personal liability in an injury lawsuit.
You seem to be neglecting the impact that insurance requirements (both personal, commercial, health, and otherwise as required by legislation) have had on this "free market for labor".
(Plus, not all markets for labor are equal in America. Try and translate your lawnmower example to the medical field, for example.)