Calculating the fair price of gold

To calculate the fair price of gold we assume that central banks need 20%-40% gold backing. Let's be conservative and use 20% gold backing.

The amount of gold that central banks hold today is $1.304 trillion.

The global base money supply is around $22 trillion today. (There are people who use M1, but I'm conservative and use base money M0)

To back this money supply by 20%, we need $22 trillion x 20% = $4.4 trillion.
This means that gold will need to rise in price from $1.304 trillion to 4.4 trillion.
Or 4.4/1.304 = 3.4 times.

This gives a fair gold price of 3.4 * $2000/ounce = $6800/ounce

AISC and Enterprise Value of Gold Miners

You want to buy the lowest cost miners with the most assets, which you can find at the top left. Although a high EV can also mean that the company's market cap is overvalued. That would mean you should buy the miners that are below the dashed lines (black, red, blue).

European banks in trouble

Here is a list of European banks and their book value. If you decide to buy banks, I would suggest that you choose from the top end of the list.