No, it's not. The cost of spending the SATs last week vs this week is that opportunity cost.

In other words, those SATs are worth more this week, and yet I could technically get more burger for the same SATs you spent a few days ago.

Sure it fluctuates, but net growth is positive over any significant time horizon.

Like think about 20k SATs in a year, worth more or less than last weeks spend?

If it's what worth more, a loss. If worth less, you gained.