roughly $160 depending on the current value gold are traded on the market on any particular day.  the Olympic charter mandates that each gold medal must contain at least 6 grams of gold.  the rest is as Isthar says made of silver and that portion of it is valued at approx. $60.

The gold medal actually mostly consists of silver with a thin cover of 99.9% gold.
But Iv got no idea the exact value of it..