And in addition to what JThomp42 said, gold really is not the only precious metal that is expensive, platinum is usually more expensive than gold.
Any precious metal that is used as jewelry and in the industries generally tends to be expensive because of its scarcity, the demand for it and its perceived value and how much others are generally willing to pay for it.
There is a real worth or market price for the precious metals like gold and platinum, which is usually listed on some sites on the internet or in the newspapers. However when these metals are used in jewelries for instance, some other costs (middlemen costs, jewelry stores cost of doing business etc) get added to them before they get to the end-user (through the jewelry stores etc) as a jewelry item or piece.
Those other costs could be as high as 25%, 50% etc or more depending on the store where you may be buying your jewelry piece from. This is one of the main reasons why when you want to resell a jewelry piece that contain such metals and/or some valuable gemstones, you may only get back a fraction of what you actually paid for it, even if you only bought the item from the stores today.
Jewelry pieces are generally valued, that is their real worth are based on the market/resale price of the precious metals (and/or valuable gemstones) in them and not on the retail price of the item in the stores.