When I was contracting at a decent hourly rate, I had to learn to calculate similar trade-offs: go buy groceries or order online, spend time picking quality produce or grab whatever quickly, drive to pick up a family member or call them a cab, etc.
When I went back to a salaried position, I had to unlearn the resulting habits, which is more painful.
Here's an interesting post about calculating the value of your free time and why it might not be as simple as some tend to think.