If something takes a lot of time (= work?), how can it be done cheaply? Or is that in the sense of waiting for a long time for the right inspiration to hit you for how it can be done cheaply?
I have a couple of minor carpentry projects going on. I could finish them quickly if I bought or rented great power tools. I don't want to spend the money though, so I'm using mostly hand tools and manual labor.
My point is that I wouldn’t say that that labor comes for free. In any case, that triangle would then not apply in a commercial setting, where you have to pay those doing the labor, in addition to it taking time.
It still applies in a lot of circumstances. For example when to buy off the shelf (for $$$$) vs rolling your own solution (which will take longer but could be less money in the long run).