The absolute BEST mines on the planet are $500. Goldcorp, for example in Red Lake Ont. Cash cost under $300, but add the cost for the mine and depletion, and overhead, and I bet you are around $500.
BTW, don't believe the coproduct/byproduct mining costs, where they mine copper and get gold as a byproduct. If the world demand for copper drops and the price of copper drops below their cost, they won't be able to afford to dig and process, so won't produce any gold.
Look for example at Novagold. They have a mine way north with 30 or 40 mm oz, but its only 1 or 2 gr per ton, and it will cost BILLIONS just to run the power line to the site. Honest to God.
So, sure, there will be deposits found and mined, especially as paper money heads to zero and the price of gold rises to where it makes sense to put more money and effort into finding and extracting it, but don't expect it to be cheap or quick.
The easy gold is either already mined or the mines are already producing. Future costs will go much higher as grades decline and costs to buy property, get past environmental roadblocks (7 to 10 yrs) and then build a mine and dig/process ore rise. In addition, taxes and royalties are going ballistic. All these things add up.
Ok, its possible there will be some huge high grade deposit found with billions of ounces, perhaps under the seabed where nobody has drilled or mined before, but what will it take to find and recover it?