There are three components to the value of an Olympic gold medal. First, there is the price that can be fetched by selling the precious metal used to make it. Second, there is the prize that is awarded to Olympic winners. Third, there are the potential endorsements that come with an Olympic win, which are not guaranteed but the next closest thing to it, particularly when Olympic winners are either marketable or rare in their countries or both.
Calculating the value of an Olympic gold medal is neither simple nor straightforward, though there are plenty of statistics out there that can be used to come up with useful estimates.