Currently, 10,000 ore mines, each with a base power draw of 50 kW, cost a total of 500 MW to run. This does not scale with the average depth of the mines: if the mines are at an average depth of 1,000, they still draw 500 MW in total.
I would expect the power draw of ore mines to scale with their average depth: deeper ore mines need more equipment to run at full speed, which increases their power draw. With 10,000 ore mines at average depth 1,000, their total power draw should be on the order of 500 GW assuming linear scaling.
A similar scaling can be applied to their maintenance costs: the deeper an ore mine is, the more equipment it needs, and the more resources are required to maintain said equipment. This scaling was present in a previous version, but has since been removed due to the deeper mines rework.