Let me start with an example where I DO understand how to find opportunity cost. Suppose I have choice to either work for firm A (\$1000 wage) or for firm B(\$2000 wage) or for firm C(\$500 wage). If I choose frim B, then I will forgo my best out of remaining alternatives, namely wage that I would get working for firm A.
Now let's add another aspect:traveling time. Working for different firms will imply different time needed to spend on traveling back and forth between my home and work. Suppose I can't monetize saved time, but I prefer to have more free time nonetheless.
I have three choices, between firm A(\$2000 wage, 2 hours traveling time), firm B(\$1500 wage, 1 hour traveling time) and firm C(\$1200 wage, 0.5 hour traveling time). Suppose I chose to work for firm B, what will be the opportunity cost of such decision? Two things confuse me in this case. There seems no clear way to pick the best alternative and then declare its effects (i.e. wage and traveling time) to be opportunity cost. Firm A offers better wage than firm C, but firm C offers lower traveling time than firm A.On ther other hand, our choice has two effects (wage and traveling time), is it really correct to take them both and declare as ONE opportunity cost, rather than two separate opportunity costs?