What is the "real" cost of mining? The way Bitcoin is set up, the cost of mining is proportional to the security of the network from a 51% attack. However, ther

What is the "real" cost of mining? The way Bitcoin is set up, the cost of mining is proportional to the security of the network from a 51% attack. However, there is no force that anchors this cost to the actual level of security needed; so the cost of mining could become arbitrarily high; and all we would have to show for it is an unnecessarily secure network. The block rewards also provide a lower bound for the (Bitcoin denominated) cost of mining and (until they resolve the congestion issues), the auction based transaction fees add to this lower bound.