… is about 0.057 U.S. Dollar on average (as of June 2020).
The computer power needed is about 200 Watts on a desktop and 50 to 100 Watts on a laptop (reference). Let us take a conservative average of 130 Watts. Running for a week, the power consumption would be 130 Watts * 24 hours/day * 7 days, or roughly 21.8kWh. Given the global average electricity price of 0.12 U.S. Dollar per kWh (reference), the cost is 2.62 U.S. Dollar.
At present, with one single mining command (that takes one CPU thread in experts’ term), it takes about one week on average to mine one STHCOIN block that contains ~11.5 coins. A CPU these days can typically run 4 mining commands simultaneously, so 46 coins can be mined in a week. The cost per coin is thus 2.62 / 46 ~= 0.057 U.S. Dollar.